There is no way to move to a wiki site in another language, unless there happens to be a corresponding page with an interlanguage link.
For example, If I'm looking at the Wikipedia article Chertsey Abbey in English, and there is no corresponding article in Bulgarian, then there is no way for me to know that a Wikipedia in Bulgarian exists at all. Of course, if I happen to know that a Wikipedia in Bulgarian exists, then I can go to bg.wikipedia.org, but not everybody knows that a Wikipedia in their language exists.
One can only know that there is a Wikipedia in Bulgarian if one happens to look at an article that exists also in Bulgarian, for example Alfred the Great. Of course, many people find a Wikipedia in their language on Google, but Google doesn’t support all languages equally well, and some people are accustomed to searching in a major foreign language (English, Russian, French, etc.) and not their own language.
There should be a way to move to any language even if an article in the corresponding language doesn't exist. This will make wikis in all languages easier to find.
What is the most effective way to do this is a question for designers and design researchers.
What we do know at this point:
- Making the existing language links compact in Wikipedia across all languages made readers click them ~90% more. (This was measured before deploying to the English Wikipedia, and this may have significant impact.)
- Surveys found that among people who speak languages other than English, the awareness of Wikipedia’s existence is lower.
- The gray interlanguage links, which are shown to editors who enabled the Content Translation beta feature are not necessarily successful at getting people to translate. This doesn’t mean that it’s doomed to failure; it may just need another round or design. For more thoughts on this, see T100344.
ArticlePlaceholder may be a target for the links, but this depends on the quality of data that Wikidata and this extension can provide. Perhaps the links to article placeholder can be shown differently?