I don’t think that’s right. I looked into the way Twitter counts characters when I was trying to work out the largest prime number that could be written out in full, in base ten, in a single tweet[1]; the rules are more complicated than you might expect, and have changed several times.

The current rule seems to be that all Unicode characters count as two, except for the ranges 0–4351, 8192–8205, 8208–8223 and 8242–8247 which count as one.

[1] In case you’re wondering, I think it’s, arguably: https://twitter.com/robinhouston/status/1197294154738544641