Are the languages arranged in recommended order of completion from left to right?
No. All three languages are chosen to be different each month and challenge in different ways. Thanks for asking 
Would it be possible to swap one of the Perl exercises for Raku to get phone-number?
Its a good one for highlighting Raku’s grammar system in my opinion: m-dango's solution for Phone Number in Raku on Exercism
Edit: Perhaps with secret-handshake? m-dango's solution for Secret Handshake in Perl on Exercism
sceret-handshake is not really an option, as you’d then have Perl featured twice in three weeks. We could swap with luhn?
Should be fine!
Consider it done!