The best alternatives to 3peat.io are Mate Translate, Google Translate, and Json2Html. If these 3 options don't work for you, we've listed a few more alternatives below.
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AssemblyAI— Speech-to-Text API with superhuman accuracy
Translate text into any language from within Slack. You can translate messages from others, your own messages, or any text. Power features include posting translations to the channel and automatically translating all messages posted to a channel.