Localization of texts works using simple text files, containing pairs of key and corresponding text.
To add localized texts, your mod should contain a folder Localization with subfolders for the language your texts are for.
Example, file <your mod>/Localization/en/Items.loca
#HazmatSuit_Name Hazmat Suit #HazmatSuit_Description An airtight, chemical-proof full body suit, designed to be used in hostile environments.
Note: Your file must have the .loca extension for the game to recognize the file. The rest of the file name ("Items" in the above example) does not matter, so you can use as many separate files as you want to keep your texts organized.
Mods are loaded in a specific order chosen by the player. If multiple mods contain a text for a key, the text from the mod loaded last wins.
To add a new language to the game, simply create a subfolder inside your Localization folder with a language code (recommended: https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes)
Note: for texts that are missing in the language the player chose, the english (en) texts are used as a fallback.