The tiles are intended to represent the C, Q, K, and W sound letters for the Catalan dialect of Spanish, but they also work for many other Romance languages such as Italian, French, Romanian, and some other languages using the Latin script. If you play in a North American Scrabble Club, you will probably find some tiles for the A, E, and I digraphs, including AEI. English-speaking players might also find a number of tiles for non-Roman scripts. The tiles are not intended to represent a specific language or script, but only a specific dialect or variety of a language.
The official Catalan letter set is given by ICORF (International Commission on Orthography for Romance Languages), which for Catalan is composed of A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, X, Y, Z, as well as the diacritics °, , «, ¬, ®, ¯, °, ±, ², ³, ´, µ, ¶, ·, ¸, ¹, º, », ¼, ½, ¾, ¿, À, Á, Â, Ã, Ä, Å, Æ, Ç, 827ec27edc