You can keep the worlds other players enter in a Json file which you can load on start of game.
And for checking the first letter of a world you can use the system expression, one of this two will do.
left(text, count)
Return the first count characters of text.
mid(text, index, count)
Return the count characters starting from index in text.
Have tried doing this in the following way:
Left(leaftext.Text,1)
I tested this by filling the text boxes that are going to be displayed inside the leaftext object with just the letters that were meant to be detected and it worked.
However, now I made the cards full words it doesn't seem to be able to detect the initials.
Not sure if i'm doing something wrong.