It is not uncommon these days for people in the Chinese community to use Chinese and English interchangeably while speaking. In Chinese, adjectives are usually followed by a de, classified as an "auxiliary word" in Chinese grammar, and somewhat like a preposition but placed between an adjective and a noun. When adjectives in English are translated into Chinese, they are also usually followed by a de, to indicate their classification as adjectives and to make them easily integrable while translated in sentences, e.g. joyful, huanle de, and beautiful, meili de. However, as people colloquially often insert English terms into sentences otherwise Chinese; in the case of English adjectives, they are also often followed by a de, even though as an English adjective, it is an unnecessary complication; and theoretically, while the commonly accepted translation of English adjectives already contains the de, it is incorrect to attach a redundant one on top of that.
The reason why people often commit this redundancy and feel awkward if without it, is probably attributed to that when people speak, their logic and thinking pattern is in a Chinese environment. The English adjectives are treated like Chinese adjectives, ripped off their English-ness. Therefore the English word in a Chinese sentence is only easily identifiable by a Chinese audience as used as an adjective when it is accompanied by a de. With the use of English widely accepted in the Chinese community, more studies into the effect of language integration and its impact on both languages are expected to be carried out.