Let’s try to understand the difference between a language and a dialect. If two people are having a conversation and they seem to be understanding each other just fine – they are speaking the same language. They may not necessarily be speaking the same dialect, but since dialects are closely-related variations of the same language, comprehension is possible. It is not so with different languages. However, sometimes dialects too are majorly distinct from each other. Cantonese, Mandarin, and Taiwanese are dialects of Chinese, but a Cantonese speaker would have difficulty understanding Mandarin as he/she would when faced with a German speaker.
The only overarching differentiator between the two is that languages are standardized written systems with literature to boot whereas dialects are predominantly oral, without any codified rules of their own or literature in existence. Dialects are not then a lesser form. A language is made up of several dialects. The difference between languages and dialects is arbitrary in nature.
Languages descended from the same linguistic family are usually intelligible by speakers of brother/sister languages. Dialects of a language vary from one geographical location to another. Both languages and dialects serve the same purpose and should be regarded equally.