Why do most of the “Japan only” models that I have seen so far have labeling in English?
This is typically called Foreign Branding.
In Japan they oftentimes use the English language to enhance the perceived value. Plus it’s aesthetic and used for imagery and less about the proper translation. That’s why sometimes the translation doesn’t really make sense.
Check out some of my BOXY posts… tons of English in mostly grammatical order
In addition to what Atxalias said, we have to consider the timeframe here. Back to the days of many of these mechanical pencils, English was the established global language and even for “Japan Only” models it was used as a mark of value as well as to minimize costs if a model is eventually resold outside the JDM. In some product circles these days, I do wonder if there are JDM only releases that have all Kanji, no English wording.
the only Kanji scripted Pentels that I know of are the Smashes in the red tubes, sold on the US and Canadian Amazon markets.
The PF509 has the Latin lettered model and lead size, but the “For Film” is in Kanji.