Full text catalog - certain value does not result in a catalog entry

Full text catalog - certain value does not result in a catalog entry

I'm confused about a Problem with a certain value in a simple table
containing addresses, that this City named "Höchst" would not be found in
a full text search
The Statement:
select id, city0
from addresses
where contains (city0, 'Höchst')
returns nothing.
Other cities with the same character "ö" (e.g. "Mönchhai") involved are
found.
So I looked at the catalog:
select * from sys.dm_fts_index_keywords (Db_id('<dbname>'),
OBJECT_ID('<dbname>.dbo.ADDRESSES'))
where column_id=25 and display_term like 'h%'
Returns the Display Terms (excerpt)
himmel 25 1
himmelpforten 25 1
hof 25 15
hoffnung 25 1
hoffnungstal 25 1
hohberg 25 1
=> There is no entry for "Höchst"
searching for 'mo%' Shows a result like
moncaprice 25 2
monchhai 25 4
moormerland 25 1
moosburg 25 1
=> There is an entry for "Mönchhai".You can see, that the 'ö' is converted
into 'o'.
Why doesn't this happen with "Höchst"?
There is not fulltext stoplist.
Can anyone help?