Here's what we know:
* He learned English during his time in England: Squanto was taken captive by an English explorer and brought to England. During his time there, he learned to speak English.
* He returned to his tribe and acted as an interpreter: He was able to act as an interpreter between the Pilgrims and the Wampanoag tribe. However, this doesn't necessarily mean he was completely fluent. He might have been able to understand and speak basic English but may not have had a full grasp of the language.
* There are no firsthand accounts of his fluency: We have no records of his actual spoken English, only accounts from those who interacted with him. These accounts are often based on second-hand information or subjective interpretations.
In summary:
Squanto undoubtedly learned English during his time in England, but it's debatable how fluent he was. It's possible he could communicate effectively in basic English, but he may not have spoken fluently.