Eudic 歐路詞典 iOS - pasting mdx (and mdd, css if available) into directory of "external custom DB path" on iOS does work - immediately adds the dict to Eudic
To set the path:
On the Eudic iOS app > top-left 3 bars > 詞庫管理 > top-right 3 dots > 設定外部詞庫路徑 > browse to a directory on the Files app > press "打開”, and the directory is set.
Mine is currently set to: Files > on my phone > 歐路詞典.