To use the translation support file, decompress it and put the contents in your Long Live The Queen directory. (So, when you're done, the translations/ folder is inside your game/ folder).
If the game finds translations (including the sample), it will add a 'Languages' button to the preferences.
The sample translation should be complete; take a look at the files in it to get a feel for how it works.
Each entry in the strings file consists of the original English version of the text, followed by the translated version. (The sample translation just translates English into English.) Lines beginning with # are comments, and will be ignored by the game. Translations MUST be in UTF-8, regardless of what text encoding your computer is using. \n in translation strings will be converted to a newline.
The default font doesn't include the glyphs used in several languages (日本語, for example); you will need to hotpatch a new font in if you want additional glyphs.
If there are any bugs, untranslatable sections, questions, or feature requests, post them publicly on the Hanako Games modding forum or the Steam Long Live The Queen forum. (Why publicly? Because that way other people who know the answer can jump in if I'm not there, and my answers will be more helpful to other translators if they're public.)
If you set persistent.log_untranslated=True in the debug console, the game will log missing translations and some other errors to translation-debugging.log, and will stick *** in front of any string that it tried unsuccessfully to find translations for.
Translations should be reasonably backwards and forwards compatible - using an old translation file with a new version will usually work (aside from the fact that strings not in the old translation file won't translate), and using a new translation file with an old version should work as long as the file translates all the strings in the old version.
LongLiveTheQueen-Translations-1.3.25.2.tar.bz2 (2016 Apr 18, for Long Live The Queen 1.3.25.1. This translation file also contains data for older versions.)
If you're working from an old version of the translation files, here are the diffs (newest-first order)
Version 1.3.21 to version 1.3.25.2. Translation-related changes: Dossiers now have {tag=male}Single and {tag=female}Single, to help with languages where the translation should vary depending on gender. Fixed a typo in one of the epilogue strings. Added translations for the new stuff on the video settings screen. The game no longer crashes if it encounters mismatched closure tags. This should work around a bug in at least some versions of the Russian fanlation. Some strings that weren't translating on the Skills and Moods pages now translate.
Version 1.3.18 to version 1.3.21. Translation-related changes: layered graphics for the moods screen and the buttons down the side of the scheduler now included in the .tar.bz2. moodbg.png now translatable. Internal Affairs 50 text changed; correct Dogs 10 text added; new Banion epilogues for delayed marriage; more tooltips for 'Show tooltips' mode on castle map.
Version 1.3.8 to version 1.3.18. Translation-related changes: Some missing conversations added. A tagged alternate version of the conversation with your mentor about extra Lumen crystals added, so languages where a conversation between Elodie and Julianna would use different honorifics than one between Elodie and Selene can have separate versions. Touchscreen tooltips translatable. Translations where the {tag= prefix was left in the translated version should no longer crash. Also, a Steam achievement crash on Windows machines (probably caused by non-ASCII paths) should no longer crash the game.
The only change between translation file 1.3.7 and 1.3.8 is the fact that '{tag=outfit}NEW' now translates directly to 'NEW'. The main game improves translation debugging, fixes a crash loading translation files, and actually includes the disambiguation for a couple of 'Of course.'s.
Version 1.2.28 to version 1.3.7. (Note: this is missing the falconry line at the beginning of newstrings-1.3.7.txt.)
String disambiguations added in 1.3.7.
Strings added between 1.2.27 and 1.3.5 (for LLtQ versions 1.3.5 and 1.3.6; if you're starting a new translation you want to wait for me to finish preparing the full translation files for 1.3.7. Which isn't out yet.)
version 1.2.24 to version 1.2.27 (for LLtQ version 1.2.27)
version 0.3 to version 1.2.24 (for LLtQ version 1.2.24)
version 0.2 to 0.3 (for LLtQ version 1.2.21)
There's also a simpler prettyprint.rpy you can use (or grab functions from), though I recommend rewriting the one in the translation package instead.
Important new translation features in 1.2.24:
String disambiguation tags, so different instances of the same string can have different translations. If a translation for the tagged version of a string is not present, it will fall back to using the untagged translation if present (so old translation files will still work, and so future additional disambiguation will be less likely to break things.)
It should now work around translation bugs related to extraneous double-spacing in strings.
There have also been an assortment of bugfixes; see the changelog for details.
Translation support was officially released as of 1.2.20.1, and was added to the main game slightly earlier. Strings which are not in the version you're playing will be ignored by the game, and strings which are in the game but not in the translation file will be untranslated (or ***'d, if you enabled logging), so you can safely use translation files for other versions of the game as long as the basic syntax is the same.