MapTiler’s OpenMapTiles pull request does install a library that changes the label language based on the language setting in user preferences. This functionality would be a useful addition to the site by helping mappers detect missing or incorrect translations, at least for the languages that would be hard-coded. However, it doesn’t sound like language support would be the principal motivation for introducing client-side style rendering in this pull request. After all, a lot of the feedback relates to gaps in language support, which the author doesn’t seem to consider a showstopper.
Maybe MapTiler recognizes that, for many of the people who have been clamoring for vector tiles on osm.org, client-side rendering would be an ego boost for the project, proof that, yes, OSM data can power a modern map too! I would challenge this notion a bit: a layperson or casual mapper who visits the site wouldn’t know the difference between a raster map and a vector map (other than a performance hit). This especially the case because MapLibre GL JS would be squeezed through a compatibility layer for Leaflet that can’t even zoom smoothly between zoom levels.
If we want to impress others and ourselves with vector maps, the map has to do more than just render in the same manner that a raster map would. For example, OpenHistoricalMap has taken the osm.org code, applied the same technique that MapTiler has proposed, and gone even further by dynamically filtering the data based on the time period the user wants to focus on. Imagine if osm.org could filter the map thematically, based on real layers like “roads”, “railroads”, and “waterways”. This is trivial with client-side map rendering.
And when we’re done impressing ourselves, maybe we can turn our attention to using vector tiles to power something a raster map truly can’t: an X-ray view that lists all the raw tags immediately when you hover over a feature. Brian’s tile server has just such a style installed. I use it all the time when developing a style based on the tiles, and I would be thrilled to use it instead of having to hop into iD just to inspect the tags on some busway or craft workshop.
In the meantime, vector styles based on vector tiles are already on osm.org – on wiki.osm.org, that is. 