I am writing a technical report with keywords which are mainly English. I am using a Glossary at the end, which describes translated keywords. Is it a replacement for footnotes or I should just keep footnotes too?
Provided you mean that footnotes are only for translations (that is, you're not using footnotes for additional information or for source citations), I'd put the glossary of translations at the beginning, and skip the footnotes. The glossary up front will alert the readers that foreign words are coming up in the text, and putting everything in one spot makes it easy to reference.
I usually find frequent footnotes to be distracting from the flow of reading, and I would imagine a technical report needs even more concentration to keep flow than a novel, so footnoting the translations repeatedly would be difficult for me.
As a compromise, perhaps the first time you introduce an English keyword, you could put the translation in parentheses right after it (as well as in the glossary).