Hi,
If uploads are failing do to issues on the client machine or the client netwrok there is nothing that mojoPortal can do about that.
If you are not forcing a specific language, the it is adapting to the user's language preference according to their web browser settings. So if its changing the button label to Japanese most likely Japanese is configured as the preferred language in the browser settings.
We ship resource files for many languages but some of them are only partially complete so for missing keys it falls back to English. That is why only some labels and buttons may be in Japanese when the user browser language is Japanese, we only have a partial translation for Japanese, so only some buttons and labels will be shown in Japanese and the rest will fall back to English.
Hope that helps,
Joe