[Gimp-user] Characters became tofu after deleting fonts on Ubuntu

[dqwyy <me dqwyy moe>]

Hi all.

I'm sorry that English is not my native language so I'm not good at it. Here is my problem.

I'm a new user on Ubuntu and I'm so excited that I can control my computer completely. Ubuntu, as a GNU/Linux 
OS is so free that I can customize it. I only use English, Chinese and Japanese so that I deleted all the 
fonts that I don't need. I think three fonts for English/western scripts are enough so I deleted all the 
fonts except Freesans, Freeserif and Freemono. I think one sans serif font, one serif font and one monospace 
font are enough. This looks really concise. I don't need to find a font on the long drop-down menu at Office 
software anymore.

Things go well until I installed Gimp. I launched gimp after installing it and found nearly all the 
characters became "tofu" (some boxes). General speaking, this only happens when lacking of fonts. However, I 
already have fonts for Latin scripts. I also have CJK (Chinese, Japanese and Korean) fonts with basic Latin 
scripts included of course. So I think Gimp use the fonts which are deleted by me, and there are something 
wrong with the fallback, too. I don't know which fonts do it use and I tried reinstall the fonts named 
"Ubuntu" to my computer (I think that "Ubuntu" font is the default font of Ubuntu, isn't it?) but nothing 
changed and I still got tofu.

So could you please help me to solve this problem? Maybe I should reinstall all the fonts which are deleted 
by me? But I can't get those fonts unless I reinstall my OS. Well, this may be a weird problem because I 
think there is nobody but me to delete so many fonts on Ubuntu. XD

My OS version is Ubuntu 18.04.1 LTS, the gimp version is 2.10.

Here are some screenshots. Thank you very much.
Screenshots:
[1. The tofu on gimp] https://i.imgur.com/PmMYVuv.png
[2. My fonts setting] https://i.imgur.com/6u8SnXV.png
[3. My font manager] https://i.imgur.com/undefined.png

Regards,
dqwyy <me dqwyy moe>
http://a.dqwyy.moe
October 5, 2018