@pras_tya The completed status is specifically for the publication status in the country of origin. It has nothing to do with scanlation progress, because this site hosts multiple languages of translations and a single status line would be kind of clunky to cover all of that (especially since anyone could start another one up in any language at any time). If a scanlation is completed, the last chapter should have an "End" marker on it in the chapter listing instead. Looks like this if you haven't seen one yet.
@Glomoro ah thank you for the info, i'm actually know about "End" mark. i'm just wanna know why there is no "End" mark while the status is complete since my filter language is english and indonesian