How to localize GeoEasy to my mother tongue?

Clone/fork the GeoEasy GitHub repo.

Make a copy of the geo_easy.eng file using the iso language code of the new language, for example for Czeh the file name should be geo_easy.cze. From version 3.1.1 language files are moved to i18n subdirectory.

FROM VERSION 3.2.0 THE MESSAGE FILE MUST USE UTF8 CODEPAGE!

Open the new file in your favourite text editor, which supports editing UTF8 (nano, vi, notepad++, etc.) and start the translation. The GeoEasy message file is a tcl source file. You should translate the text between quotes in the assignment statements. In tcl assignment statements start with set reserved word.

You can check whether you made a syntax error trying to load the translated file into the tcl shell:

tclsh geo_easy.cze

Add the new language to the geoLangs array in the geo_easy.msk:

array set geoLangs {hun hu eng {en us} ger {ge de} cze {cs}

and add the Windows language code to _langCodes array in geo_easy.msk

array set langCodes {"040E" hun "0409" eng "0407" ger "405" cze}

Start GeoEasy on a system where the default language is the new language you have added or start GeoEasy with the --lang command line switch to select the new language:

GeoEasy --lang cze

Create a pull request to send back your translation.