Click on System Tools to expand the sub-menu. In version 11.x, the Language option is typically the second or third item from the top of this sub-section.
TP-Link hardware often uses regional designations (like -RO- or -US-) which can restrict language options. Change Language in TP-LINK TL-WR841N (RO) v11.x, How To Change Language in TP-LINK TL-WR841N -RO- v11.x
If you only see one language (e.g., only Chinese), your router may have : Click on System Tools to expand the sub-menu