When I say that really fast I get "facid".
"fa" then "swid" - which in Welsh i'd pronounce "sooied"
I still dont get how you translated that, but i'm glad I have a handy way to remember the Spanish word for Tuna now.
Translating English into Welsh or vice versa by recognition of the word just doesn't work as Welsh is closer in grammatical structure to European languages and closer in word form to Klingon. It's like trying to recognise your dinner after it's been processed by your body, some things just aren't meant to be done. Given that the purpose of Welsh is to not be English this isn't entirely suprising - but I guess maybe for a Spaniard it is easier to grasp.