src/Mod/TechDraw/Templates/ISO/localized/README.md

This folder (locale) contains translations for TechDraw workbench templates in the parent Templates folder. The name of each locale subfolder represents a language, which follows IETF BCP 47 standardized codes. The original TechDraw templates in the parent folder are written using American English (en-US).

As such, the most basic name for a locale subfolder will include an ISO 639 language code (e.g. de for German). If it's necessary, additional subtags can be added to describe language variants. For instance variants spoken in a particular country, or a specific script. Those subtags are combinable and are based in other standards.

The most common additional subtag is an additional country code to describe a regional variant of the language (e.g. de-DE for German spoken in Germany, es-AR for Spanish spoken in Argentina, or zh-CN for Simplified Chinese in Mainland China). Country subtags are based on the ISO 3166-1 standard's country codes.

To add a translation:

1. Add a folder named ll or ll-CC (where ll is a 2-letter or 3-letter ISO 639 language code, and CC is a 2-letter ISO 3166-1 country code).
2. Copy over the TechDraw templates in the parent Templates folder that you want to translate to your new folder.
3. Translate away!
4. Submit a PR (GitHub Pull Request) to get your Tech Draw template translations included in FreeCAD.

Use the FreeCAD forum if you need further help.