i've researched IMDB guidelines on help page
We use the original title of a movie/show in its original language as it appears on screen (on the title card) in the opening credits. So all alternative titles found on posters, DVD boxes, reference books, trailers, websites, re-releases, etc. are irrelevant. They do NOT define what the primary title should look like. All titles must include the year of first public screening enclosed in ()'s as explained further below.
so from my interpretation, the main title is supposed to be the original but romanized titletherefore
https://www.imdb.com/title/tt9015178/ should be called "Gojira"
here is this title on the site of the production company, where it says that the original title is ゴジラ the katakana for go ji ra
https://www.imdb.com/title/tt0087344/ meanwhile godzila 1985 was a usa release and should have "Godzilla 1985" as the main title it was re-released in japan on home-video later and was back translated as Gojira 1985 https://stat.ameba.jp/user_images/20110817/21/chikori-ta2011/be/e3/j/o0600044511423970409.jpg
so it can in no way be named just "Gojira"