Vexing font issue with PowerPoint for MacOS fixed.

I still use PowerPoint on my Macbook for presentations (because it supports inline mathematical equations, something Keynote doesn't does, but with an ugly math font and weird baseline). People that know me a little, know that I am a bit of a font and graphic design freak. So I freaked out when all of a sudden some fonts I often use on my slides (Swis721 BT, a Helvetica variant, and Futura BT for example) stopped working.

I run Mac OS Catalina (10.15.3) and PowerPoint for Mac (version 16.35). I'm on the 'Insider Slow' update channel for Microsoft Office. At some point after some update, I could no longer insert new text with the above fonts on my slides. Old slides with text using those fonts still showed fine. I could still use templates based on these fonts to create new slides. I could even cut text from Word styled using those fonts and paste them into a slide. The fonts also showed fine in the font selection menu. The only thing I could not do was create a new text box, type some text, and then select a Swis721 BT or Futura BT font variant to style the text accordingly. PowerPoint would simply ignore the command and keep the text at the default Theme font. This only happened for a small subset of fonts (which happened to include some fonts I use often, which is why it bugged the hell out of me).

I struggled finding a solution for a long time. Nothing seemed to work. Clearing the Apple font cache? Nope. Clearing the Microsoft Office font cache? (Even the latest versions of Office appear to have separate font caches for each application, in e.g. <user>/Library/Containers/com.microsoft.Powerpoint/Data/Library/Application Support/Microsoft.) No way. Prioritising certain fonts for Office? No luck.

I finally found the answer today…

I decided to take a closer look at the differences between the fonts that I still could and the ones that I could no longer use in PowerPoint. So I opened Font Book and compared the detailed information of these fonts. And this is where I discovered that the fonts that didn't work where exactly the fonts that didn't have 'Dutch' (my native tongue) as a supported language. (Now there is an interesting question as to why these particular fonts say they do not support Dutch but do support any other language with a Latin alphabet, which probably has to do with the symbol 'ij' (i.e. i followed by j) that is treated as a letter in Dutch. The fonts in question indeed do not have that glyph.) From this the solution followed. I checked the language settings for PowerPoint, and discovered that no default language was set. Setting the default language to English solved my problem: I can finally insert new text on my slides using my favourite fonts again.

P.S. Strangely enough, even setting the default language to Dutch works, so the problem seems to be with not having a (default) language set at all.