Linux oracle => odbc => PHP umlaut问题

I have an Oracle DB with varchar2 fields that store umlauts. I also have a PHP-application that connects to the DB via ODBC. The whole thing runs on Linux.

The Problem with the Umlauts is now that they are converted to normal letters, e.g. ä => a, but only in the PHP-Application and the isql program. If I use sqlplus or the Oracle web GUI, everything works fine, which tells me that the problem lies in the odbc connection.

I just don't know how to configure ODBC so it uses the right encoding...

Edit The connection is done via

odbc_connect(DSN, User, PW)

I understand that the DSN corresponds to the configurations in either /root/.odbc.ini or /etc/odbc.ini.. which I'm not entirely sure, since I haven't set up the system and I have no experience with ODBC at all. At the moment the DSN is "NAPA", the /etc/odbc.ini file has following settings:

[NAPA]
Driver = Oracle 11g ODBC driver
DSN = OracleODBC-11g
ServerName = localhost
UserID = *****
Password = ****
NLS_LANG = AMERICAN.WE8MSWIN1252
Charset = utf8

The DB parameters are

SQL> SELECT * FROM NLS_DATABASE_PARAMETERS;
+-------------------------------+-----------------------------------------+
| PARAMETER                     | VALUE                                   |
+-------------------------------+-----------------------------------------+
| NLS_LANGUAGE                  | AMERICAN                                |
| NLS_TERRITORY                 | AMERICA                                 |
| NLS_CURRENCY                  | $                                       |
| NLS_ISO_CURRENCY              | AMERICA                                 |
| NLS_NUMERIC_CHARACTERS        | .,                                      |
| NLS_CHARACTERSET              | WE8MSWIN1252                            |
| NLS_CALENDAR                  | GREGORIAN                               |
| NLS_DATE_FORMAT               | DD-MON-RR                               |
| NLS_DATE_LANGUAGE             | AMERICAN                                |
| NLS_SORT                      | BINARY                                  |
| NLS_TIME_FORMAT               | HH.MI.SSXFF AM                          |
| NLS_TIMESTAMP_FORMAT          | DD-MON-RR HH.MI.SSXFF AM                |
| NLS_TIME_TZ_FORMAT            | HH.MI.SSXFF AM TZR                      |
| NLS_TIMESTAMP_TZ_FORMAT       | DD-MON-RR HH.MI.SSXFF AM TZR            |
| NLS_DUAL_CURRENCY             | $                                       |
| NLS_COMP                      | BINARY                                  |
| NLS_LENGTH_SEMANTICS          | BYTE                                    |
| NLS_NCHAR_CONV_EXCP           | FALSE                                   |
| NLS_NCHAR_CHARACTERSET        | AL16UTF16                               |
| NLS_RDBMS_VERSION             | 10.2.0.1.0                              |
+-------------------------------+-----------------------------------------+