I have tried to fix my own but couldnt that than i came to your discord and they suggest someting but didnt solve here is my problem.

When i start my server than try to join it while server is opening (not quite opened yet) this errors comes to console

is it a big deal or not

https://paste.insprill.net/iwofoyejaq.rb

This is because Player#getLocale() didn't exist up until 1.12(.0) so what LP is doing (trying to) is try to get the locale in a way that didn't exist back then! Before that there used to be Player.Spigot#getLocale() but it was introduced in 1.8(.0) (something easily fixable tbh); there is no fix for this issue for the Bukkit Legacy build of LuckPerms other than just gracefully falling back to English.

what should i do now couldnt understand. Maybe using another spigot ?

is that issue a big deal or not what happens if i dont fix

If you want to 100% avoid the issue you can use an older version of LuckPerms for Spigot (before v5.2, you can find those in the resource page in spigotmc.org) but this issue can be fixed with ease.