it's not the fonts which cause these issues, it's the fontconfig configuration on your system, which prefers certain fonts over others in specific situations. As the ja_JP setting in fontconfig-voodoo is optimized for Japanese users who do not use extended Latin characters, this is indeed expected behavior. If you prefer DejaVu or any other font fir Latin script, I suggest that you copy /etc/fonts/conf.avail/69-language-selector-ja-jp.conf to ~/.fonts.conf, then edit this file and add the DejaVu or other font entries at the top of each font list for serif, sans-serif and monospace. This should fix your problem.
Thomas,
it's not the fonts which cause these issues, it's the fontconfig configuration on your system, which prefers certain fonts over others in specific situations. As the ja_JP setting in fontconfig-voodoo is optimized for Japanese users who do not use extended Latin characters, this is indeed expected behavior. If you prefer DejaVu or any other font fir Latin script, I suggest that you copy /etc/fonts/ conf.avail/ 69-language- selector- ja-jp.conf to ~/.fonts.conf, then edit this file and add the DejaVu or other font entries at the top of each font list for serif, sans-serif and monospace. This should fix your problem.