Hi Luigi
This is no issue related to the database and just peripherally to OpenSimulator istself, rather to the operating system.
E.g. on a Linux system, you can see with the shell command "printenv" your enviroment vairables. If you see there any language related variable (such as LANG, LC_NUMERIC, LC_COLLATE or similar) NOT having a value starting with en_*, then it might be worth a try to change this.
Greetz
FoTo50