Java I18N Checker
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I18N Checker

I18N Checker is an internationalization and localization tool for Java.

It can be used for verifying strings in Java sources and resource bundles. Also serves for exporting all strings for translation and importing them back to resource bundles. Current implementation works with well-known structure of directories (as we have developed it for our own repository which is organized this way).

The tool startup parameter is "top level dirs" list. Each top level directory should contain modules and each module is recognized using "src" subdirectory. In this example the top level directories are "modules_group1,module_group2":

|   +---module1
|   |   +---src
|   |   |   \---com...
|   \---module2
|       \---src
|           \---com...
|   +---moduleAAA
|   |   +---src
|   |   |   \---com...
|   \---moduleBBB
|       \---src
|           \---com...


Main class is org.i18nchecker.I18nChecker. It has several setters and some executable methods.

Currently I18N Checker works in a few different modes, depending on what properties are set (or what method is called). TopDirs and RootDir properties are mandatory.

  • Mode 1 - Print errors: prints all errors in I18N (no other extra property is required)

  • Mode 2 - Export to CSV for translation (language and exportToFile property must be set)

  • Mode 3 - Apply translated CSV into translated resource bundle files (language and importFromFile property must be set)

  • Mode 4 - Run as unit test verifying that there are no regressions in I18N. runAsTest method should be called and it takes all required parameters.

  • TODO: Mode 5 - like Mode 1, but from command line (i18nchecker.jar should be executable)


See this project build script. It uses playground directory as example of incorrect sources/resources bundles. Run i18n-consistency-check target from build.xml.

Also see this project's unit test - it shows how I18N Checker can run as unit test (to prevent i18n regressions). Test should pass as some i18n errors are expected. Try to add one more i18n error to sources in playground and run the test again. It should fail.

General rules for writing correct code

("Correct" in this context means compatible with this tool.)

These strings are ignored by I18N tools in Java sources (it means you don't need to write NOI18N comment there):

  • strings where str.trim().length() <= 1
  • strings which are in the same line as Java annotations - e.g. @SomeAnnotation("this is ignored")
  • strings which are in the same line as "assert" keyword
  • strings in comments of course

All other strings must be commented with NOI18N including (but not only these):

  • logger messages
  • exception messages (it depends! Think a little about each message. If it's supposed to be printed only to log file then do NOT translate it. If you think the exception message can be shown to user in error dialog, then translate)
  • all other strings which are intentionally left in English only

Other rules:

  • Do NOT use NOI18N for strings which actually are translated and are in
  • Do not use cross-package resource bundles. All strings in sources must be localized only in in the same package.
  • Tool will report error when string is in, but is not present in any Java source in this package. In the case that you are sure string is used (key is composite - for example NbBundle.getMessage(..., "LABEL_" + someKey)) then mark these string with #YESI18N above the string in

Note: we can change these rules in the future. Feel free to propose changes (e.g. what else to ignore in Java sources, etc.)


See also Geertjan's blog post about this tool. You can find more details there.

Contact me if you have any comments: petr (dot) hamernik (at) gmail (dot) com