Apparently the word "string" can't be blocked. Something with the code of the addon?

(if you're guessing why I want to block it, it's because people on my country/server can't say my character name right - Striding - without mispelling or shortening it wrong) and that's the only that can't be blocked.

There's nothing in the code blocking specific words, only specific symbols.
Is the problem that you can't add it, or that it's added but not working?

it's added, with a bunch of variations, and it doesn't block on chat

The "string" is cut at the top.

Can you elaborate on "people"? This addon only filters public chat and yells, and only if they aren't your friend, guild member, etc.

So that's why it's not blocking: "friend, guild member, etc.", that must be it.
By people I mean players on my region/country that doesn't know english that well.

Yes anyone that's potentially friendly (guild member, friends list, in your group) will not be filtered. This addon is mostly designed to clear up random public chat.