That one page with Tingyu looking at Akio? Breathtaking.
I really should have checked the last update date before starting
Welp
Even assuming that Ian has his tongue completely cut off, he should actually be able to speak more than he does, actually. The tongue is important for articulating certain sounds, but it's not vital for every single one of them.
There are several consonant sounds that Ian wouldn't be able to produce (like t, d, l, r, s, z) because they involve the use of the tongue, but there are some others (like m, b, p, f, h) that don't involve it. Even then, with certain consonant sounds that do typically involve the tongue (such as a hard g or a k) there are other sounds that are close enough to them to be used as a replacement (for the examples I previously mentioned, using a uvular pronunciation or even a glotal one).
As for the vowels, it would also not be totally impossible to get around without a tongue. We're shown that since Ao's name is just two open vowels, it's not hard to pronounce for him (as an experiment, try sticking your tongue out or puting it in a weird position inside your mouth and not moving it when you say it, the sound will be a bit distorted, but it's still intelligible). My guess is that he'd have no trouble with open vowels, struggle with semi opened and semi closed vowels, and struggle greatly with closed vowels. How hard or how easy it'll be for him to adapt will depend on how important the distinction between vowels is in the language he speaks and the particular set it requires. Nevertheless, even when using different vowels because of his limitations, it should be no different from trying to understand someone with a thick accent. Yeh ken even mek eet whet E'm treen teh seh eseng enle een vewel, ken't yeh?
It would certainly take some training and he'd probably need to look for synonyms here and there, but he should be able to communicate successfully, even more so provided he has people around him that are willing to put in the effort to understand him using context clues when his pronunciation deviates too much from the standard.
(=・ω・=) I might be overthinking