You can use a character class instead of a sequence. eg:

$ perl -MTest::More -e 'ok (/\b\p{XPosixAlpha}+\b/, "$_ matches") for 
+(qw/A Z Å Ä Ö/); done_testing();'
ok 1 - A matches
ok 2 - Z matches
ok 3 - Å matches
ok 4 - Ä matches
ok 5 - Ö matches
1..5
$
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