Upload the .srt or .vtt file to Presentr Analyze, choose Translate subtitles and the language. Each line is translated and keeps its exact timing, so the new file lines up with your video. You download the translation as SRT and VTT.
1 credit per minute of subtitles. If your credits cover only part of the file, the lines in that part are translated.
No. Every line keeps its start and end time; only the text changes.
Yes. From the run you can turn the translated subtitles into a voiceover timed to the same lines.