The Retrofit Mod intself is localised and contains French translations for almost all in-game text. If you have French M2TW installed, the Retrofit Mod installer will automatically install the French assets. The Unit addon mods may not be localised and may overwrite some of the localisation files with English ones (e.g. unit descriptions, etc for the new units).
To create a french translated unit add-on, you would probably need to replace the overwritten retrofit text files with the original retrofit text files and merge all the required unit descriptions and text for the unit addon from the various unpacked kingdoms campaigns french text files.
You will need to back up any files you modify in case they become invalid, and you will need to determine exactly which new text entries are required for the retrofit mod text files (by comparing the original retrofit mod text files against the unit addon text files).
You can use any parts of the Retrofit Mod in other mods, but you need to ask the author of the Grand Unit Addon for permission to use their work.
Unspoken Knight
