The grammar and vocabulary of these languages are quite similar, but the spelling and pronunciation are different, especially Manx spelling.
See Irish phonology for an explanation of the symbols used and Irish initial mutations for an explanation of eclipsis. Letter s. Modern spelling can be used with the Gaelic typeface and punctum delens, but this is extremely rare - mostly you can count on all books in Gaelic type being in the old spelling.
The Gaelic written alphabet used in Irish literature is an adapted form of the Latin alphabet. Whether this includes Northern Ireland is not clear.
Modern loanwords also make use of j k q v w x y z. However, one influence from Gaelic is the way many Irish people pronounce the letter 'a'.