I wrote "Welsh seems hard" -- no need to say "the Welsh language" in this context. I know, it's in beta...
I'm guessing that it disliked "seems". I bet "Welsh looks hard" would have been accepted
"The Welsh language SEEMS hard" sounds more natural in English. In general, "looks" would be only used where something can actually be seen. "Seems" works for both material and abstract entities.
Since there is a village, called "Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch", I believe this statement XD