> I never saw those old tags in StreetComplete.

It doesn't show them, to keep it simple for inexperienced users. It correctly removed other tags you can't see (branch, opening hours, phone, website) so I'm surprised it didn't remove wikipedia and wikidata tags.

> I had to tap the "plus" icon to add the new web address. 

The plus icon is only to add names in other languages. The "International" (int_name) tag is used in Bulgaria to add the name transliterated to Latin script (i.e. it is still Bulgarian language but Latin script according to the official transliteration law)