I've been looking at this too because I want to make a sort of proofreading/editing mod. I will note that Translator++ , which has a good free version, sort of works and has a very usable interface. It appropriately handles the vast majority of Map[number].rxdata files. Unfortunately, it cannot load Fieldnotes.rxdata or PkmnAnimations.rxdata (unclear why), and although it seems to handle Map051.rxdata (the character-creation scene) correctly, using the translated Map051.rxdata file breaks the character creation process. It is also possible that there are other issues that I simply haven't noticed yet.
Unfortunately, Translator++ does not create a translation option in the same way that TranslationManager does. So even if the issues with Translator++ can be resolved, it still may be a suboptimal solution.