I tried a map of Japan on a Garmin Nuvi 2639, and for Southwest Japan (Kyuushu) most road names came out as Chinese pronunciations written out in Pin-yin system. For example, a canal would display as Kuchuan, while the Japanese pronunciation would be Horikawa.
It seems that this is an issue with all names written in kanji (i.e. chinese characters) as opposed to Katakana (i.e. syllabic writing). For example, a store name コスモス薬品 has the first four symbols are syllabic, and the last two are written by Chinese characters.
The syllabic reading is correct (kosumosu), the Chinese characters are not (yaopin instead of yakuhin).
It would be best if the original tags in Japanese were kept (as is the case on the web interface at openstreetmap.org), instead of transliterating them into the English alphabet.
This situation is the same on both Garmin device and in the Basecamp application.
It seems that the proportion of the names appearing in Chinese is lower in other places, for example in Tokyo.
When a Garmin map is created with a specific character set (typically a character set based on the Latin alphabet), names must be “translated” into that character set. That is no problem for English names, and most other languages written in a Latin-based alphabet. In other cases, an English version of the name may be provided in the data (e.g. name:en=Tokyo), then that can be used.
In all other cases, some “translation engine” is used. For classical Chinese characters (i.e. also Kanji), it uses the Pinyin transliteration.
Please note that the problem is not with Japanese only. Also Indian alphabets (including Thai) show issues of that translation process (there it is wrong order of vocals relative to the consonant).
I just dropped in on this sub-forum, although I’m not a Garmin map user.
I don’t understand why there should should be a phoneme order problem with Indic scripts as Unicode encodes them in the order of pronunciation, even though, say, the short i sound in Hindi is written before the consonant that it phonetically follows. A character by character transliteration should produce the correct transliterated order.