Meltype Switches Japanese/English Input Without Half/Full-Width Key

Every time English words are mixed into Japanese text, typing comes to a halt. For technical writers, this has long been a habit. According to Nobuyoshi Kodera, the author of the ITmedia column, Japanese conversion engines try to turn characters typed in romaji into Japanese, so entering an English word requires either switching to English mode or pressing the Muhenkan key (or F10 key) after typing. The resident tool “Meltype” aims to reduce this very operation. Rather than replacing the conversion engine, it separates whether the typed characters are Japanese or English before input: English is entered as is, and only text judged to be Japanese is passed to the conversion engine.

Attempts have been made gradually along the way. “ATOK” implemented a feature that treats a word as English when its first letter is typed in uppercase with Shift, and the author hoped this would finally let him skip the extra steps. However, brand names that do not start with a capital letter, such as “macOS,” still required separating each word and pressing the Muhenkan key. Japanese conversion began evolving rapidly around 2025, and the column has covered azooKey on macOS, which was first tested in July 2025, followed by Copilot Keyboard for Windows and ATOK Ver. 36. Meltype is another approach that emerged within this trend.

The Windows version is distributed as a prebuilt installer, so installation is easy. However, the conversion engine is the standard “Microsoft IME.” When the author used it, no switching between Japanese and English was needed, and typing continued smoothly. Yet most Japanese text is typed in Japanese input, and that part depends entirely on Microsoft IME. The author's assessment is that frequent misconversions of homophones and errors in phrase breaks mean that “overall conversion efficiency has improved only in a small part.” The column also notes that Microsoft's “Copilot Keyboard” is now available in an official release, and it expresses hope for support for it in the future.

The Mac version is a preview and requires building from source. The author asked the AI Codex to build it, and the AI fixed a link error caused by an outdated definition file. The conversion library used is “AzooKeyKanaKanjiConverter,” a kana-kanji conversion engine based on dictionaries and statistical cost calculation. The current azooKey, on the other hand, uses “Zenzai,” a neural kana-kanji conversion system, and in the author's view Zenzai is superior in conversion efficiency. In fact, compared with azooKey 0.1.4, which the author normally uses, Meltype seemed to produce more misconversions.

So what changes if you use it now? For people who mix English into their writing, the benefit comes down to the disappearance of switching effort. The Windows version is easy to install and reduces the hassle around English words. Conversion accuracy for Japanese text remains at the level of standard IME. The Mac version was said to offer promising conversion accuracy, but in the author's testing it produced more misconversions than azooKey 0.1.4. It is still in preview and is aimed at users who can handle building it themselves. Japanese conversion technology is still being reshaped, and it is not yet clear which conversion engine Meltype will ultimately settle on.