The date pattern and decimal point from the language is not honored in the Swing client. It works in ZK-client.
This only occurs if "Add missing translations" hasn't been run for the actual languange.
See screen shots for example. Tested on latest revision a3dc84b05b91 (dated 22 june 2013).
The following warning appears in the log:
12:14:59.249-----------> Env.verifyLanguage: Not System Language=Language=[Svenska,Locale=sv_SE,AD_Language=sv_SE,DatePattern=YYYY-MM-DD,DecimalPoint=false] - Set to Base Language en_US 
The System Language flag is set on Swedish but there are yet not translations to Swedish.
The question is if you should allow a locale for dates and decimal points even if there are no translations yet? Perhaps it has other implications.
The code controlling this is in Env.verifyLanguage.