The `parameterize` method uses the `I18n.transliterate` method, whose
documentation says:
```
I18n.transliterate("Ærøskøbing")
=> "AEroskobing"
I18n.transliterate("日本語")
=> "???"
```
That means we can't use it for dictionaries where characters don't have
a transliteration to the latin alphabet.
So we're changing the code in order to only transliterate characters
with a transliteration to the latin alphabet.
Note the first example ("Česká republika") already worked with the
previous code; the test has been added to make sure accented characters
are handled properly.
cd58b96fad