I frequently update installed OS/2 versions from (Warp4 to ArcaOS 5.0.4) to the latest using Suntan Special.. But this is English-only. Still, if installing English updates (everything I use is included, not just the operating system) would help a non-English system, I'd guess that could help.
It's a lot of work to update, and I think Suntan Special does not save much time, but does help to remember all the items that need updating.
Installing English updates, e.g. a latest OS/2 Warp 4 FixPak for OS/2, is a matter of choice. If the OS doesn't change, and you are officially one of the happy few (eCS 2.x: DE, eCS 1.x but not eCS 1.2R: DE/IT/NL), then the numbr of language issues is limited. For one because of having lost a lot of countries and languages.
I'm compiling a "full" installation manual at the moment, to not have to remember everything. It's longer than expected. I still have to install a few apps and still have to configure (e.g. sometimes setting or checking the language) almost all apps, but so far language-related changes are: keyboard selection during the install if it's not US-International, change or check the WIN-OS/2 keyboard if it's a Dutch (and perhaps other) keyboard, install a "language update" for *.MAH files, and change a translation error (WPPrograms' title "Eeditor"). I could change many names ("Lokaal Systeem" -> "Lokaal systeem"), but that's overdoing it. Language packs of FF/SM are included in a profile backup. Most of the individual INSTALL.CMD /INSTALL.EXE files have been moved to 12 INSTALL.CMDs, which may sometimes use a translated parameter string or title ("[Which driveletter?]" -> "Welke stationsaanduiding?]"). Install WIN-OS/2 printer driver with a right language, if available. That's it, so far. Also caused by the fact that we've (almost) lost a few communities (e.g. Italy, Japan, ...), so it's hard to avoid English software, and you'll need many "users" for a translation. I'm one of the happy few, with rather active translators. I'm not sure if I would/could buy ArcaOS NL tough, especially if legacy stuff doesn't always work properly anymore. Anyway, the hardest part of installing a supported foreign OS will typically be that you'll have to select the option in the middle instead of having to recognize "Laat het toetsenbord gezellig de grootte van de beeldschermresolutie van de opdrachtaanwijzing zelf bepalen". eCS does mix languages, but that's quire rare. CMD.EXE's "yes"-prompt, instead of "ja", comes to mind. Presumably the Korean OS/2 Warp 4 FixPak is the most impressive one, because it's not IBM's.