Subtitling and dubbing are two different processes which can be applied on a video. Subtitling helps in applying a text box at the bottom of the video. This text represents the audio of that video in written format. The language of this text may vary dependent on the type of subtitling required for that video (same as that of audio or different.
On the other hand, dubbing is the audio effect of that video in a different language.
Let us understand the difference with this example. You are watching a movie in German language and you understand English, but not German. Now, with the help of text of those dialogues in English, you can understand the movie, but listen to the dialogues in German. In case of dubbing, an English speaking actor will only act as the voice-over-artist for the dialogues spoken in German. He will translate the audio in English. This helps in catering to both German as well as English movies.
the language of subtitles in the video is different than the one being spoken in the video. The benefit of inter-language subtitling is that a new target audience can be selected for the video. This helps in multiplying the audience by many-folds depending on the number of languages in which the audio is translated. It is important that the correct translation is employed. Therefore, an experienced translator can only be good at subtitling.
It refers to the creation of subtitles in the same language as that of the current video. This helps in case different dialects of the same language are used across the country e.g. Chinese. It also helps in the building and retention of vocabulary of language, which in turn can impact the literacy rate of majority people speaking that language and being able to read the same through subtitling.