Creating language files for localization
Localization in SAGA is done by a so-called language file, which is actually a text file containing two columns (tab separated): one with the English version of the text (parsed from source code) and one with the translation. The language file must have the extension *.lng. On windows, it is sufficient to place the file in the main folder of the SAGA binary installation directory, where it is recognized automatically. On other OS, such a file can be specified in SAGA GUI with the Language Translations parameter of the Module Libraries Settings. After a restart of SAGA GUI, the translation file will be used.
Binary releases of SAGA (at least the windows versions) include a saga.lng.txt file in the main path, which can be used to create a new language file (the file is also available in the source code, see below). It only contains the first column (English). Simply load it with a text editor or with SAGA GUI and add your translations.
There are several developer tools available to create and handle translation files. They are build into the module library Development Tools, which is available in the SAGA sources. The module library contains three modules:
Extract Translatable Text Elements from Sources: This module can be used to create a new English template file. The module parses the SAGA sources for translatable text and creates the English column of the translation file.
Import Translations: This module allows to import existing translations from a file into a more recent language file.
Merge Translation Files: This module allows to merge translation files into a single file containing all unique entries.
Existing language files are available in the sources under saga-gis/src/saga_core/saga_gui/res.