**List of steps to reproduce** (step by step, including full links if applicable):
* Open https://en.wikipedia.org/wiki/Special:Search.
* Copy this (with a space at the end): `абвгдеёжзийклмнопрстуфхцчшщъыьэюя ` (it's the Russian alphabet).
* Paste into the search form as many times as you can.
**What happens?**:
At the 4th paste, you will bump into a length limit. But it's a wrong one – 129 characters, which is obviously 255 bytes (Cyrillic characters are 2 bytes each).
**What should have happened instead?**:
The real limit is 300 characters, see T107947 and [[https://en.wikipedia.org/w/index.php?title=Special:Search&search=абвгдеёжзийклмнопрстуфхцчшщъыьэюя+абвгдеёжзийклмнопрстуфхцчшщъыьэюя+абвгдеёжзийклмнопрстуфхцчшщъыьэюя+абвгдеёжзийклмнопрстуфхцчшщъыьэюя+абвгдеёжзийклмнопрстуфхцчшщъыьэюя+абвгдеёжзийклмнопрстуфхцчшщъыьэюя+абвгдеёжзийклмнопрстуфхцчшщъыьэюя+абвгдеёжзийклмнопрстуфхцчшщъыьэюя+абвгдеёжзийклмнопрстуфхцчшщъыьэюя&ns0=1|a 305 character query]]. Actually, you //will// be able to reach it if you type in the address bar, not the search bar.
**Other information**
I noticed `mw.widgets.TitleWidget` is used there with its 255 byte limit. So perhaps this limit is wrongly inherited by the `mw.widgets.SearchInputWidget`.
Came across this bug when people [[https://ru.wikipedia.org/wiki/Template_talk:Cite_web#Упростить_штрафные_категории|started renaming long categories]] because their names don't fit in the search query.