The Welsh word for "week" is wythnos, which means eight nights. This is because they count seven days, plus the six nights between them, and the one before and the one after.
Can someone who speaks Welsh count sefirah in Welsh after the first six days? If you say "today is 7 days which is one wythnos" (according to google translate, "Heddiw yw saith diwrnod, sy'n un wythnos, o'r Omer", don't ask me how to pronounce that), you're not being accurate, since the eighth night is no longer part of the seventh day.