What translanguaging actually means
Translanguaging is not code-switching (unconsciously switching languages) and not translation (converting from one language to another). It refers to the practice of using all available linguistic resources flexibly and purposefully to communicate and learn.
García and Wei (2014), who developed much of the translanguaging framework, argue that multilingual speakers don't have two separate language systems - they have one integrated linguistic repertoire that they draw on differently in different contexts. Forcing artificial separation of these systems in educational settings may not reflect how language actually works in the brain.
This doesn't mean first-language use in ESL classrooms is always productive. It means the question is more specific: which uses of L1 support acquisition, and which ones avoid the productive struggle that acquisition requires?
When L1 use supports speaking development
Meaning negotiation during pair work. When two students speaking the same L1 briefly switch languages to clarify what they mean before returning to English, this is often productive. The L1 is used to establish shared content, which then enables more complex English production. "Wait - do you mean X or Y?" in L1 followed by a longer English elaboration is a reasonable communicative strategy.
Planning before speaking tasks. There is research evidence that allowing students to plan in their L1 before producing in L2 results in more complex, fluent English output than either planning in L2 or not planning at all. This suggests that for teacher-assigned preparation time before speaking activities, L1 planning can be permitted without undermining the English production goal.
Explaining complex concepts to lower-level students. In multilingual classrooms where students share an L1 and there is a significant level range, allowing a more proficient student to briefly explain a concept to a lower-level student in L1 can unlock participation that wouldn't otherwise be possible. The alternative is the lower-level student sitting out the activity entirely.
Processing emotional content. When speaking activities involve personally significant topics - family, identity, significant experiences - some students find it genuinely impossible to discuss in L2 with the emotional authenticity the topic requires. Brief L1 expression of the emotional core, followed by L2 elaboration, is preferable to either emotional detachment or avoidance.