I am not sure how much you know about editing mods, so I am giving a brief summary here:
1/ Here I choose Schall Uranium Processing as the example here, which have more of the details I need to talk about. (Thus the SchallUraniumProcessing_0.17.5.zip file.)
2/ In your mods folder (For Windows: C:\Users\{name}\AppData\Roaming\Factorio\mods), decompress the ZIP file with the same folder name. If doing correctly, file thumbnail.png and subfolder locale can be seen under folder mods\SchallUraniumProcessing_0.17.5.
2A/ Please move the ZIP file to other places. (e.g., a "Reference" folder) Otherwise the game may not load your locales made in the following steps.
3/ Go into subfolder locale\en, you will see a file uranium.cfg. It is a pure text file in UTF-8 format. Open it with a decent text editor. (Do NOT use Windows Notepad!!! Use something much better like "Sublime Text" or "Notepad++ to do text editing!)
4/ In the file, you will see lines starting with:
[item-name]
uranium-concentrate=Uranium concentrate
uranium-238=Depleted uranium
uranium-low-enriched=Low enriched uranium
uranium-235=Highly enriched uranium
The whole file is in English locale. The four lines are the English name of the items. The "value" part of each line is what you need to translate.
For example, in German (en) I translated it into:
uranium-concentrate=Urankonzentrat
uranium-238=Abgereichertes Uran
5/ You may start with English (en), German (de), or any language you are more familiar with. You can also compare them to see how things work.
6/ BTW, do not modify these files directly. Clone one of these subfolders, and rename it as nl (internal code for Dutch). So the file under edit should be locale\nl\uranium.cfg.
7/ Note that there are some wrapped text (called magic strings) that do NOT require translations:
EN: uraniumprocessing-uranium-238-colour-change=Colour change __ITEM__uranium-238__
DE: uraniumprocessing-uranium-238-colour-change=Farbwechsel __ITEM__uranium-238__
The magic strings are in format of __A__B__. A is the type, which can be ITEM, ENTITY. B is the internal name (key) of the entry to be referenced to. In this examples, it refers to [item-name] > uranium-238, which is line 3 of this file. So line 20 will display in game as:
EN: uraniumprocessing-uranium-238-colour-change=Colour change Depleted uranium
DE: uraniumprocessing-uranium-238-colour-change=Farbwechsel Abgereichertes Uran
8/ Lines under [mod-name] and [mod-description] are optional, since the game do not use the localized versions of them BEFORE you are actually using mods. So very limited uses. So I did not make such lines in German locale.
9/ Start the game. Pick Dutch in your game language (supposed you already did), you will see your strings showing! So you can check if string format / spacing / grammar / word order work as you expected.
10/ If finishing, you only need to send this file locale\nl\uranium.cfg. I will include it into my mods.
PS: I am actually thinking of putting all the community localizations into a new mod (name as "Schall Mods Language Pack"?). So the localizations can be updated independent of my mods.
