I am currently investigating the use of the Multilingual plugin on a large (750k+ topics) forum that wants to have a number of foreign-language subcommunities.
When the multilingual plugin is enabled and a user has chosen their language(s), the topic list will be almost empty. This is happening because the plugin will currently show only the topics that have been tagged with a selected language (as opposed to hiding topics that have been tagged with an unselected language).
I have looked through the documentation on here and in the topic on Meta and it seems that the only way of currently setting this up is to bulk tag all topics (or bulk rebake all topics and have language detection via the translator plugin enabled).
I see this as a big impediment for people to use the plugin since the setup effort becomes really high, and also there is no point in tagging all 750k+ existing topics if they’re all English. We would have topics disappear for users that happily select Spanish without realizing that it will impact the visibility of existing topics they have been participating in.
Now I know I’m the product manager on here 
but I am asking this for a client I do not have much prior knowledge of and experience with the plugin (yet) so I am asking this because maybe there is prior history or a certain design decision that I’m not aware of.
Would a PR be welcomed and/or useful that
- allows showing topics without a language tag on a forum wide basis, i.e. a site setting “show topics without a language tag”
- allows showing topics without a language tag on a user specific basis, i.e. a user preference setting below “content languages”: “show topics without a language tag”