Transliteration of non-Latin scripts
CartoType's tool for creating map files, makemap, can transliterate Russian and Greek names into the Latin alphabet automatically. The maps above show part of Thessaloniki, Greece, before and after automatic transliteration. As you can see, the street names in the map on the right are followed by versions in the Latin alphabet.
Most names in the OpenStreetMap data are in the local form only. We solve this at data preparation time by adding automatic transliterations into the Latin alphabet and tagging them as 'name:en', but only if no 'name:en' attribute exists. So where a transliteration or translation has been done it is preserved.
You can ask makemap to transliterate from Greek or Russian by using these command-line options:
for Greek: /transliterate=gr
for Russian (cyrillic): /transliterate=ru
Japanese
You can convert Japanese names into their Latin-alphabet (romaji) equivalents using a freely available dictionary of Japanese names, JMnedict.xml. Here is a page with a download link and a link to the terms of use, which require only an acknowledgement.
To use the dictionary just add its file path to the command line. For example
makemap imabari.osm ../japanese/JMnedict.xml
Here is a before and after image showing the results. The map on the right contains about ten more Roman-script placenames.