Look at the File menu item Save All. Under either
JDK 1.3 or 1.4 it puts the underscore under the
'a' in "Save". This is wrong; the menu item in the
bundle is listed as:

Save &All

Under JDK 1.3, there is nothing to be done. Under
JDK 1.4, however, we can use
setDisplayedMnemonicIndex. The current logic in
Actions is wrong; it calls sDMI only for non-Latin
characters. It should use it for *all* characters.

There are other potential logic errors in this
area (#26678 patch). The logic to catch linkage
errors in Actions14 is wrong; instantiating the
class *will not* generally throw
NoMethodFoundError under JDK 1.3 (depends on VM
validation settings and so on). You need to
actually try calling the method to determine this.
See my comments in #26678.

Also there is weird code that turns off the
mnemonic in case the strings ends with '&' - what
is this for?

Seems to work as desired for me on Linux under JDK
1.3.1_03 and JDK 1.4.1_01. Needs confirmation on
other platforms, and especially in localized (e.g.
Russian) builds.