Translation versus copywriting
Translation refers to the process of converting the content in a given language (source) to another language (target).  The translator should have thourough understanding of both the source and target language involved and the target language should be the native tongue.  The translator will translate the source language content into the target language without adding, omitting or deviating from the given source content.

The translator has to keep the translation as close as possible to the source content, in spite of the lack of similar words or appropriate phrases, commonly experienced while translating in different languages.  The translator's hands are tied down by the limits and scope of the content given in the source language and can in no way rewrite, extrapolate or define in any other way than the given source content, however good the intentions might be.

The translator's attempt to rewrite, extrapolate or define the content in the source language may render the translation useless and has the potential to irreparably damage the purpose of translation.

Copywriting
Copywriting is the art of developing content and write-ups in a very creative way based on the given source content, giving due considerations to the pre-defined objectives, purpose and target audience.  Copywriting naturally imbibes the cultural and geo-political nuances of the specific language (also the source language). Copywriting is required when creating content for marketing or publishing and in all cases when the content is going to be read by several people.

Comparison of Translation v/s Copywriting

Copywriting does not involve translation and requires the copywriter to rewrite, extrapolate and even add to the given source content.  A copywriter needs to have a creative temperament as opposed to the methodical disposition of a translator. Copywriting is a secondary process to translation as translation process creates the source content on which the copywriter can work.