Wrong cursor position in terminal with two or three bit UTF-8 characters (like umlauts)

I often work with librelec over terminal and have an issue which drives my crazy:

When I have a line in the terminal with an umlaut and move the cursor over it the terminal looses the cursor position.

This only occurs with Libreelec and not with other systems I remote to.

Example (with _ indicating cursor position)

LibreELEC:~ # üb_

Move cursor all the way left

LibreELEC:~ #_ üb

Move Cursor all they way right

LibreELEC:~ #üb_b

If I use a thai unicode character (which requires three bits to encode) the line shifts by two positions each time.

This makes it very difficult to rename a file for example.

Anybody knows what causes this and how to fix it?

I tried:

Different Terminal emulators like Konsole, xterm, xfce-terminal

Setting environment vars LC_CTYPE and LANG to en_US.UTF-8