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OPUS-CAT is a collection of software which make it possible to OPUS-MT neural machine translation models in professional translation. OPUS-CAT includes a local offline MT engine and a collection of CAT tool plugins.



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December 3, 2019 09:28
January 26, 2021 23:38

OPUS-CAT MT Engine and CAT plugins

OPUS-CAT MT Engine is a Windows-based machine translation system built on the Marian NMT framework. OPUS-CAT MT Engine makes it possible to use a large selection of advanced neural machine translation models natively on Windows computers. The primary purpose of OPUS-CAT Engine is to provide professional translators local, secure, and confidential neural machine translation in computer-assisted translation tools (CAT tools), which are usually Windows-based. To that end, there are plugins available for two of the most popular CAT tools, SDL Trados Studio and memoQ (OPUS-CAT can also be used in the Wordfast CAT tool as a custom provider). OPUS-CAT MT Engine provides pretrained MT models for a very wide selection of language pairs, courtesy of the OPUS MT project (listing of OPUS MT models).

Note: The documentation below is for the earlier iteration of OPUS-CAT, which was branded Fiskmo MT. OPUS-CAT documentation is currently being added to a new site. To install the latest MT Engine and plugins, go to

Quickstart for translators

  1. Download the Fiskmo MT Engine and install it to your computer by extracting it in a folder on your computer.
  2. Download the plugin for your translation software and install it:
  • Trados 2017: double-click plugin file to install.
  • Trados 2019: double-click plugin file to install.
  • memoQ 9.2 or older or memoQ 9.3 or newer: Copy the plugin file to the Addins subfolder in the memoQ installation folder. IMPORTANT: Make sure to unblock the dll file before copying it (right-click file, choose Properties, check the Unblock box in the bottom right of the Properties window). Detailed memoQ instructions.
  • Wordfast: There is currently no plugin for Wordfast, but Fiskmo MT can be used in Wordfast as a custom MT provider (this requires some configuration work, so contact Fiskmo project for assistance if you wish to use Fiskmo with Wordfast).
  • OmegaT: There is an OmegaT plugin available for the development version of the MT engine. The plugin will be released shortly, but if you want to use the OmegaT plugin before that, contact us.
  1. Start the Fiskmo MT Engine application by clicking FiskmoMTEngine.exe in the extraction folder.
  2. Install models from the Fiskmo model repository for the language pairs that you require.
    • Click Install OPUS model from Web.
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    • Enter source and target language codes in the filtering boxes on the top row, select a model (usually the one with latest date suffix) and then click Install locally.
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  3. After the model has been downloaded and installed, test that it works.
    • Select model and click Test selected model.
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    • Enter translation in the Source text area, click Translate and wait for a translation to appear in the Translation area (producing the first translation may take some time, as the model needs to be initialized, subsequent translations are faster).
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  4. Start your CAT tool, and add the Fiskmo plugin to a translation project.

NOTE: Fiskmo MT Engine application needs to be running on the computer, when the plugins are used.

Fine-tuning models with the Trados Studio plugin

Fiskmö Trados 2019 plugin includes a functionality for fine-tuning models with bilingual material that is specific to a domain or style of translation.

The base models that can be downloaded from the OPUS model repository generally produce useful machine translations. However, since the base models have been trained on a mix of different bilingual texts from various textual domains and styles, the translations may not be suitable for many contexts. In a professional translation setting in particular, there is an expectation of terminological and phraseological consistency within documents and adherence to style guides and glossaries.

By fine-tuning a model with suitable fine-tuning material (bilingual texts from the relevant domain), a base model can be modified to produce translations that adhere to the conventions used in the fine-tuning material.

The fine-tuning functionality in the Trados 2019 plugin is implemented as a custom batch task. The batch task can be invoked via the Batch Tasks button on the Home ribbon (or via context menus):


The fine-tune batch task can also be used to pregenerate the translations for the project. Note that this means pregenerating the translations in the cache of the Fiskmö MT engine so that they will be instantly available as matches when translating in Studio, the translations will not be copied in the sdlxliff files by the custom task. You may choose to fine-tune and translate, fine-tune only, or translate only (the model will have to be selected in that case). The different modes are shown in the following picture:


Fine-tuned models are identified by model tags (see the Model tag box in the picture above), which usually describe the model. Fine-tuning settings can defined more specifically in the Fine-tuning settings tab:


Generally the most useful fine-tuning material is the translated text that is already present in the project (i.e. exact match segments). These segments will always be extracted for fine-tuning. However, you can also extract fuzzy matches from the TM to use as fine-tuning material, which is especially important in cases where there's not enough translated text present in the project. You can set the minimum fuzzy percentage and the maximum amount of fuzzies to extract for each segment in the Fine-tuning settings tab.

When you are ready to start fine-tuning, click Finish in the Trados Batch Processing screen. Extracting the fine-tuning material may take a while, depending on project and TM size. Once the fine-tuning material has been extracted, the batch task will send it over to the Fiskmo MT engine running on the same computer in order to start the fine-tuning.


The fine-tuned model will be shown in the local model list with a status of Customizing, and the text Fine-tuning in progress is displayed in the bottom of the MT engine screen. The fine-tuning will generally take several hours, and once it's finished, the status of model will change to OK and the text at the bottom will disappear.

You can use a fine-tuned model for translation by selecting the tag of the model in the settings of the Fiskmo translation provider in Trados:


If the fine-tuning is still in progress for the model with chosen tag, the connection status message will state so.

If the project contains a lot tags, it's possible to include textual representations of tags into the fine-tuning material, in which case the fine-tuned model learns to transfer tags from the source text into the target text. The tag learning feature is experimental, so it might not work optimally in all cases (the fine-tuning material needs to contain enough tags to learn from, and the tag structure should be relatively simple). You can choose to learn placeholder tag positions (Include placeholder tags as text) and tag pairs (Include tag pairs as text).

Installing a zipped model in the MT engine

Models are normally installed in the MT engine with the Install model from Web functionality, but they can also be installed from files. This is useful for distributing customized models and for installing models in systems where no Internet connections are possible. To install a zipped model, click Install model from zip, browse to the location of the model zip in the file system, select the model zip, and click Open.

Using the Fiskmo plugin in memoQ

Installing the memoQ plugin

  1. First download the memoQ plugin file: memoQ 9.2 or older or memoQ 9.3 or newer.
  2. IMPORTANT: Unblock the FiskmoMTPlugin.dll file:
  • Right-click the file and choose Properties.

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  • Check the Unblock box in the bottom right and click OK.

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  1. Copy the FiskmoMTPlugin.dll file to the Addins subfolder in the memoQ installation folder.

The path of the installation folder varies in different memoQ versions, for memoQ 9 the default installation folder is C:\Program Files\memoQ\memoQ-9.

Here's the easiest way of locating the memoQ installation folder:

  1. Press the Windows key to open the Start menu with the cursor in the search box.
  2. Type "memoq" into the search box.
  3. You should see a link to the memoQ application as the top result.
  4. Right-click the memoQ link and choose Open file location.
  5. The folder containing the link opens.
  6. Right-click the link and choose Open file location again.
  7. The memoQ installation folder containing the Addins subfolder should now open.

Once the FiskmoMTPlugin.dll file has been copied to the Addins folder, the plugin should be loaded when memoQ is started. As the Fiskmo plugin for memoQ is an unsigned plugin, you need to confirm that it can be loaded with memoQ. Select Yes in the dialog box:


Setting up the Fiskmo plugin for memoQ

MT is used in memoQ by first defining a set of MT settings and then attaching those settings to a project. You can create a set of MT settings by performing the following steps:

  1. Open Resource Console by pressing Alt + R.
  2. Select MT Settings from the bottom of the Resource pane on the left and select Create new from the bottom right pane.
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  1. Enter a name and a description for this set of MT settings, and then click OK.
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  1. Select the MT settings you just created in the Resource Console and click Edit settings.
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  1. Scroll to the bottom of the list of MT plugins and then check the box next to Fiskmo MT Plugin.
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  1. Click the gear icon next to Configure plugin.
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  1. In the Fiskmo MT plugin settings window you can check that the Fiskmo MT Engine is running on the same computer by clicking Retrieve language pair information.
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  1. If memoQ displays an error when you click Retrieve language pair information, Fiskmo MT Engine is probably not running on your computer. In that case, start Fiskmo MT Engine as instructed in steps 3 to 5 in Quickstart for translators.
  2. Click OK to finish editing the settings (the OK button may be hidden by the Windows taskbar, but you can still select it by pressing Alt + O). Close Resource Console by clicking Close.

Adding the MT settings to a translation project

To use MT during translation, you need to add the MT settings that you created in the previous section to the translation project. You can do this performing the following steps:

  1. Open the project and select Settings from the bottom of the Project home pane on the left.
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  1. Select the MT icon from the ribbon in the Settings pane and check the box next to the MT settings you defined previously (here named Fiskmo MT settings).
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  1. When you now open a document for translation, translations from the Fiskmo MT Engine should be displayed in the Translation results pane (if not, close the file and open it again).
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Pretranslating with Fiskmo plugin for memoQ

Often it's best to pretranslate documents with the Fiskmo MT plugin before starting translation, since this means that the translations are available immediately (when translating segment by segment in the editor, generating the MT may take some time).

You can pretranslate documents with the Fiskmo MT plugin in memoQ by performing the following steps:

  1. Open the project, select Translations from the Project home pane on the left. Right-click the document you want to pretranslate and select Tasks and Pre-Translate.
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  1. In the Pre-translate and statistics window check the **Use machine translation if there is no TM or corpus match ** box in the Machine translation section. Fiskmo MT should be listed as a MT plugin in this section.
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  1. Click OK to start pretranslation. When you open the document again, each segment with no TM matches should contain a machine translation with a match percentage of 0.
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Using the HTTP API for integrations

It's possible to obtain translations from the Fiskmo MT engine via an HTTP API. Note that the HTTP API is not enabled by default, as doing so requires system administrator permissions. To enable the HTTP API, open the command prompt as an administrator and use the netsh utility:

netsh http add urlacl url=http://+:8500/ user=DOMAIN\user

(Substitute your domain and username for DOMAIN\user. 8500 is the port number used by the HTTP API.)

Translations can be fetched from a local Fiskmo MT engine instance with requests using the following format:


A list of available language pairs can be fetched with requests using the following format:



This work is part of the fiskmö project. It implements a self-contained MT plugin for SDL Trados Studio that runs a translation engine based on MarianNMT locally within the plugin. Please acknowledge the project if you use our tools and resources.


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MIT License

Copyright 2019 Tommi Nieminen

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.



OPUS-CAT is a collection of software which make it possible to OPUS-MT neural machine translation models in professional translation. OPUS-CAT includes a local offline MT engine and a collection of CAT tool plugins.








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