Our Linux OAS should be started using the same NLS_LANG as client is using, in our case NLS_LANG=SLOVAK_SLOVAKIA.EE8MSWIN1250

export NLS_LANG=SLOVAK_SLOVAKIA.EE8MSWIN1250

cd $ORACLE_HOME/opmn/bin

# restart OAS
./opmnctl stopall
opmnctl: stopping opmn and all managed processes...

./opmnctl startall
opmnctl: starting opmn and all managed processes...

Assuming that there are eastern european characters used in your FMB files in labels, etc..
You need to recompile all the PLL(libraries), MMB(menus), FMB(forms) files using the following:

# this is required
export ORACLE_TERM=vt220

# For PLL files we need to use
# NLS_LANG=AMERICAN_SLOVAKIA.EE8MSWIN1250
# otherwise you get nasty compile messages.

export NLS_LANG=AMERICAN_SLOVAKIA.EE8MSWIN1250

for x in *.pll
do
$ORACLE_HOME/bin/frmcmp_batch.sh module=$x \
userid=user/pass@TNS_NAME batch=yes module_type=library
done

# For MMB and FMB files we need to
# use NLS_LANG=SLOVAK_SLOVAKIA.EE8MSWIN1250

export NLS_LANG=SLOVAK_SLOVAKIA.EE8MSWIN1250

for x in *.mmb
do
$ORACLE_HOME/bin/frmcmp_batch.sh module=$x \
userid=user/pass@TNS_NAME batch=yes module_type=menu
done

for x in *.fmb
do
$ORACLE_HOME/bin/frmcmp_batch.sh module=$x \
userid=user/pass@TNS_NAME batch=yes module_type=form
done

Note: Using this example above, you DON’T need to set DISPLAY variable.