dead key text input broken

What locale are you using, what keyboard layout do you use in Windows?

Locale: Latvian, keyboard layout: Latvian (aposthrope)(by Tilde ltd.) Keyboard layout has one dead key "'".

Some more data: when locale is Japanese and keyboard layout is Latvian (similar to previous), it is completely impossible to input any modified characters, inkscape completely refuses to input "'"key (pressing "'" and "a" in sequece produces just "a"; presing "'"key once or multiple times, does not inputs anything)
These data are on version 0.46 win32 and system locale is Japanese, and Keyboard layout is Latvian (by Laacz (http://laacz.lv/f/misc/apos/apostrofs_punkts_vista32.zip)(can be downloaded here))

Changing locale to Latvian, exactly replicates in first description described problem (this bug appears to be independent on exact type of dead key keyboard layout).

Also, when using Japanese locale and Japanese keyboard layout, bug [https://bugs.launchpad.net/inkscape/+bug/166632] is still present (IME input box is located near corner of program window, not at the text input site)(however Japanes text input works properly)(except of this visual issue).

also, windows was windows xp sp2 english version (non localized)

Dead key (with apostrophe key as dead key) based keyboard layouts are the most popular form of inputting Latvian language texts in computers, athough these layouts are not an official standart and are not bundled with windows.

OK. Some investigation reveals the suspected - Inkscape does not rely on Windows to deliver the correct characters. Polish keyboard layout in Windows uses tilda (~) as a dead key for Polish characters and while it works as expected in Windows it does not in Inkscape since it uses GTK input method based on the LOCALE set when Inkscape starts.

Some pointers:
http://webcvs.freedesktop.org/xkeyboard-config/xkeyboard-config/symbols/lv?view=markup
http://gitweb.freedesktop.org/?p=xorg/lib/libX11.git;a=blob;f=nls/en_US.UTF-8/Compose.pre
http://blogs.gnome.org/simos/2008/01/30/improving-input-method-support-in-gtk-based-apps/

It seems we need to enable lv_LV locale in Inkscape.

Does this problem still exist in the current release version (Inkscape 0.47)?

Yeah, just tested in 0.47. All attempts yield character with ' on top, instead of correctly modified character.

Still present in Inkscape 0.48.2 (Windows Vista 64bit). I've got a custom keyboard layout with the locale de-AT. Some deadkeys work but not others, e.g. ^,j = "ĵ" ; ^,w = "ŵ" as expected, but ^,t and ^,ß [sharp S on German keyboard] do nothing while they should produce "ṱ" and "ẞ", respectively.
Some combinations produce wrong characters, e.g. ^,1 = "¹" instead of "¼" ("¹" should be the output of AltGr+´, 1) Some aren't recognised as deadkeys at all, e.g. AltGr+c and AltGr+Shift+7 should be deadkeys but produce a character right away. Undefined deadkey combinations do nothing at all, e.g. ^,q should produce "^q" but does nothing.