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Tighten up condition to generate suggestion

There aren't many examples where this makes a difference. One that I know of is
isolated underscores, where it would suggest a "W". This change would also
prevent isolated groups of numerals from generating a suggestion, although they
are ignored via a regex supplied in app.rb.
Add "cymraeg" to ignore list

It's the correct Welsh for 'Welsh', but is generating a suggestion.
Don't suggest for "romania"

It generates a suggestion of "Roumania" which is not the spelling used on GOV.UK.