You can adjust the font size manually if it's not shown correctly.
(Avoiding the GUI settings menu here to save you from deciphering the text)
1) Close Minetest
2) Open the file
minetest.conf in your Minetest directory with any
good text editor, like Geany / Notepad++
3) Add and increase the value of the setting "font_size" and "font_size_mono" (for the ingame chat logs) until it's displayed correctly.
Your phone or window isn't wide enough to display the code box. If it's a phone, try rotating it to landscape mode.