1: If a player writes on the hanging plates in any language (For example: Russian, Arabic, etc.), except English (after all, it was fixed in recent versions, for English, except for other languages), then 15 letters will be written. Although the hanging plates should fit all 10 letters.
2: In Java edition, hanging plaques work well, and despite which language you wrote the text, 10 letters of this language are placed there.
3: The screenshots show that when I wrote (in Russian, the letter "г"; in Arabic, the letter "ع"), 15 letters fit on the hanging plates, and 10 should.

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Edit: (by magwar )
Pasting the additional info from comments, by Jervie20:

This causes the symbols counts over 15 "€" symbols same with "⌈" and "ɛ" according to screenshot, A "§" can causes off-center the text and "π" Has limited up to 7 characters

1. Place using any hanging signs
2. Write using "ɛ", "€" or "⌈" symbols around
3. Count the character to see happens