It is extremely common for Japanese software to contain English, sometimes containing almost exclusively English. As someone who formerly imported hundreds of Japanese video games from roughly the same timeframe (1987-1995) I’d say 75% of them were either entirely in or mostly in English.
I always assumed it had something to do with the character set; English has only 26 characters, save punctuation and numerals. A Japanese character set has, at least, hundreds. The developers could never be sure exactly what characters might be supported in their customer’s hardware. If they did everything in Japanese, they ran the risk of their software being unintelligible if any given customer’s hardware didn’t support all the characters they were trying to use. If they wanted to use a device’s built-in character set, English characters were a pretty good bet to be included universally, regardless of where the hardware was from. This was the only way they could be sure to avoid using unsupported characters, unless they designed custom character bitmaps to be included in their software.
