The webinstaller should offer the end-user with all languages, and show some warning if the chosen one is not installed.
Web installer states: "Please pick your language from the following list. If your language is not listed, please inform your systems administrator." Perhaps the message can be changed, suggesting a way to add more languages before proceed. Bug 12017 adds proper description to "present" (i.e. installed) languages on web installer. But to show a complete list without using database you will need a hardcoded TT list of language codes, it's doable. An then a JS validity check for selected vs. present language.
(In reply to Bernardo Gonzalez Kriegel from comment #1) > Web installer states: > > "Please pick your language from the following list. If your language is not > listed, please inform your systems administrator." > > Perhaps the message can be changed, suggesting a way > to add more languages before proceed. > > Bug 12017 adds proper description to "present" (i.e. installed) languages on > web installer. > > But to show a complete list without using database you will need a hardcoded > TT list of language codes, it's doable. > > An then a JS validity check for selected vs. present language. We could calculate everything on the .pl and let the page be a static one.
I think maybe the easier route would be to make the note/hint more visible and explain about it affecting which language the sample data will be installed? The most common mistake here might be people thinking it only affects the language the web installer displays in.