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The Japanese app-defaults file for Netscape 4.73 included in netscape-common-4.73-1.i386.rpm (a recent update) is broken. When LANG is set to ja, netscape-communicator starts, but the menu strings do not show up in the top area, among other places.
The previous posting was inaccurate. The bug in netscape-{common,communicator}-4.73-1.i386.rpm was that netscape refuses to run when LANG is set to either ja_JP, ja_JP.eucJP, or ja_JP.ujis. (I only get the license agreement dialogue and nothing happens after that.) When LANG is set to ja, netscape starts, but then a lot of menu strings are missing. This behavior was the same with netscape-4.72, so it's not really the problem.
I can't reproduce this with the current package (4.74-4); running netscape with 'LANG=ja_JP.ujis' shows the menu items in Japanese.
The same problem persists with netscape-{common,communicator}-4.74-0.6.2 for me. I have found that I can avoid the problem by copying the Japanese app-defaults file that came with netscape-common-4.72 to my home directory (changing the string "4.72" to "4.74"). With the app-defaults for 4.72, netscape-communicator-4.72 runs normally with LANG set to ja_JP.ujis.
I *still* can't reproduce this, with LANG set to ja_JP.ujis, netscape runs in japanese fine. Make sure you don't have any rogue app-defaults files lying around.
What I meant in the last posting was that netscape-communicator-4.74 (not 4.72) works fine with the old app-defaults file from netscape-common-4.72 (with the string "4.72" replaced by "4.74" everywhere). No, I don't have any rogue app-defaults files. I have a few netscape-related lines in my .Xdefaults file, but that shouldn't be the problem because the problem disappears with the old app-defaults file. I'm running netscape-communicator-4.74-0.6.2 on Red Hat Linux 6.2J, so the setup is not completely the same as yours. Looking at the differences between the app-defaults file of 4.74 and that of 4.72, I do suspect that the problem is due to the new app-defaults file.