Welcome - the most important thing to remember with this word in standard English is that it is NOT followed by the preposition IN, which is the typical mistake made by the speakers of just about every other European language, but by the preposition TO, as in Welcome TO Europe, Welcome TO Košice, Welcome TO the 12th international symposium...

Other languages have their own equivalents (bienvenu, willkommen, dobrodošli), but it looks like those speakers view their words as phrases, integral units which are not analyzed grammatically, but simply used in practical situations when visitors arrive IN a place. The English idea is still based on the grammar, "come" as the third form of the strong verb "to come - came - come", so as it's usual to say "Come to our party" or "Come to Košice and fall in love", because "come" means "movement TOwards us", so you should say "Welcome TO Slovakia" and "Welcome TO U. S. Steel Košice".