ISO-8859-11 is basically exactly identical to TIS-620, with the added
non-breaking space character.
Basically our detection will always return TIS-620 except for
exceptional cases when a text has a non-breaking space.
With the new case_mapping lang property, we can consider upper and lower
case versions of the same character as one character.
This makes sense in some language, and would allow to enter some rarer
characters (but still in the main alphabet) inside the frequent
character list. For instance 'œ' and 'Œ' in French.
