As already mentioned in some of the issues, the Block is not visible in some languages.

#4337 Blocks and warnings should be fully visible in the sidebar.
#4737 In some language, the width of the blockly block canvas is not enough, so can't see characters on blocks

This is because the width of the Block Palette is fixed.

I am also trying to add a new customized Block (longer width), but it is very difficult to see.

This has been an issue since about 4 years ago, and I would appreciate it if you could address it.