Q: Is it ethical to translate a published article into another language and publish it?

Generally speaking, journals are not in favor of publishing content that has already been published, even if it has been published in another language. However, this is not unethical as long as you maintain complete transparency on this matter. The ICMJE guidelines have a section on Acceptable Secondary Publication that should be maintained for such publications to be ethical and acceptable. I quote this section here:

Secondary publication of material published in other journals or online may be justifiable and beneficial, especially when intended to disseminate important information to the widest possible audience (e.g., guidelines produced by government agencies and professional organizations in the same or a different language). Secondary publication for various other reasons may also be justifiable provided the following conditions are met:

• The authors have received approval from the editors of both journals (the editor concerned with secondary publication must have access to the primary version).
• The priority of the primary publication is respected by a publication interval negotiated by both editors with the authors.
• The paper for secondary publication is intended for a different group of readers; an abbreviated version could be sufficient.
• The secondary version faithfully reflects the data and interpretations of the primary version.
• The secondary version informs readers, peers, and documenting agencies that the paper has been published in whole or in part elsewhere—for example, with a note that might read, "This article is based on a study first reported in the [journal title, with full reference]"—and the secondary version cites the primary reference.
• The title of the secondary publication should indicate that it is a secondary publication (complete or abridged republication or translation) of a primary publication. 

Note that as per ICMJE, secondary publications may be deemed justifiable if they are intended to reach a wider audience. Therefore, you should mention in your cover letter why you feel your research findings should be disseminated globally and how it will benefit a global audience. If your argument is convincing enough, the journal might agree to publish the paper.

Once you find a suitable target journal, please mention the previous publication of the manuscript in another language in the cover letter for this journal. Please also clearly highlight the new data that you have added to the English manuscript to emphasize the novelty of this paper. This might also make a case for separate publication of the English manuscript.

Related reading:

• Can I republish my Japanese article in English?
• Can I publish two papers in different languages using the same data and methods, but as a more elaborate version?