I found keyboard layout switching to be too much friction.

I am programming in English and writing in English and German. What I use now is the UK international layout with dead keys. Plus compose key bindings for less frequently used symbols like € or °. This allows me to keep the same layout everywhere, which makes my life easier - and typing faster.

I quite often switch between multiple European languages, and can basically type any character in any of them using a US-international layout, with dead keys.

I can make all French and Italian accents, German Umlauts, and put a Tilda on the n for the Spaniards. Both uppercase and lowercase letters.

Sounds like a business opportunity for you.

Yeah just learn the EURKEY layout and you won't ever have to switch it.

That sounds very interesting and very complex, but I guess you might only need to target the languages that use similar character sets to English. I don't know enough about Asian languages to comment on them.

I don't have this issue due to my second language having a very different character set and dialect.