After some digging I did indeed find what I believe is the article. As mentioned I read about in American Scientist (IIRC), but based on the abstract this must be it. From the abstract:

By the time of the test, children of all ages had acquired most of the vocabulary necessary to describe the target event. Despite this, they did not translate preverbal aspects of their memory into language during the test. In no instance did a child verbally report information about the event that was not part of his or her productive vocabulary at the time of encoding. We conclude that language development plays a pivotal role in childhood amnesia.

I also found this follow-up study by someone else[2], again from the abstract:

This research suggests that children cannot independently translate preverbal memories into words even with extensive task support. Therefore, language acquisition may indeed play an important role in the offset of childhood amnesia.

However this[3] recent paper argues that this effect might only be relevant for strategic recall, where the kid is asked to recall the memory, but not spontaneous recall which happens involuntarily.

Of course, I imagine spontaneous recall isn't very useful for recalling what you've studied in your home country...

[1]: https://doi.org/10.1111/1467-9280.00442 Breaking the Barrier? Children Fail to Translate Their Preverbal Memories into Language

[2]: https://repository.lib.ncsu.edu/handle/1840.16/1427 The Sound Barrier: Two-Year-Old Children's Use of Newly Acquired Words to Describe Preverbal Memories

[3]: https://doi.org/10.1016/j.dr.2022.101050 Spontaneous verbal recall: A new look at the mechanisms involved in episodic memory retrieval in young children

I read about it in American Scientist IIRC, my as for my dad I don't know but he portrayed it more or less as common knowledge in the field.

I'll do some digging, check back in a day or two.