Demo data and languages

There is a mismatch between the languages configured for demo data and the data created for the demo data. Demo instance can have e.g. fi, en but data like titles are generated for fi, en and sv always.

- [x] only generate test or demo data for the languages in use (i.e. parameterize by the languages) (#3057)
- [ ] check that you are able to edit an item that has extra translations (e.g. data with fi, sv, en and if you save it it will have only the configure languages e.g. fi, en.)

NB: there are some tickets about how the UI doesn't work so well when a language has been dropped, e.g. #2932

Start by reproducing a demo instance configured with fi and en, using an item that has fi, sv, and en translations. Check the edit-and-save flow; done means saving the item leaves translations only for the configured languages, while the completed generation task remains covered by #3057.

Written by the indexing model from the issue text.