As per CLDR this language (gv) has only one plural form
<pluralRule count="one">n mod 10 in 1..2 or n mod 20 is 0</pluralRule>
But, in MW, we have 4 plural forms
Form 0 = n mod 20 is 0
Form 1 = n mod 10 is 1
Form 2 = n mod 10 is 2
Form 4 = everything else
This is not at all compatible with CLDR.
We can inspect how the plural forms are currently used and contact linguists and native speakers to verify. Depending on the results we can consider whether we can handle these with 1=foo exceptions or whether we need to push a change to CLDR.