BrillanNording
commented
7 months ago Addendum: Linux Libertine G already has this behaviour (at least for German), which I believe constitutes yet another reason that Libertinus, as the de facto continuation, should implement it as well.
When Libertinus was originally forked from Libertine (version 6.0), what once constituted ss01 became the default glyphs for Ä, Ö, and Ü, while the original defaults in turn became the new ss01, with the reasoning being that the new default follows a “more conventional” form. In reality however, neither form is more conventional universally; it depends entirely on the function that the two dots serve. When serving as diaeresis, the new default is entirely reasonable. When indicating umlaut on the other hand, having the dots closer to the letter is more sensible, which is the reason why this was the default in Libertine to begin with (please see this page). Furthermore, some languages (including my native tongue of Swedish) have these glyphs as separate letters entirely. While I cannot speak for every language, the old default felt a lot more natural when typesetting Swedish.
For this reason, I suggest enabling ss01 by default for German and Swedish at the very least, just as ss07 already is for Swedish (changing the shape of Ŋ). It might also be worth considering doing this for all languages which use Ä, Ö, and Ü for umlaut or as separate letters instead of diaereses. If I am not mistaken, this would include at least the Nordic, Uralic, and Turkic languages.