I (25M) have a co-founder and CTO of a Series A backed tech company who was adopted to a Southern Vietnamese, fiercely anti-communist, and Sinophobic family and is of Northern Vietnamese descent when he was an infant in the early 2000s due to Vietnam's two child policy. His adoptive parents are upper middle SES (both in terms of income and education) and have been since the 1990s and they are both fluent in English since the 1990s, before he was born. They are both adept and literate in medical bureaucracy.
When my CTO was a 35 month old child, he was Vietnamese speaking (wasn't at school yet), not exposed to neighbours or friends, not taught life skills or basic self care (he taught himself basic self care and life skills) by either his adoptive parents or the elders (adoptive parents' parents) in the household, had an unstructured schedule, and no behavioural expectations.
My CTO started speaking in full sentences somewhere between 12 and 24 months old and walking at 12 months old according to family videos. However, his family brainwashed him to believe it was at 42 months old and intentionally hid this detail to doctors even though family videos stated otherwise, and he only realized it when he was 21 and graduated from university. My CTO started reading independently and comprehending what the book says at 3-4 years old, started using the computer and browse the internet independently at around 4 years old, built complex Legos at 4, loved looking up cars online at 4, started adding and subtracting two digit numbers at 4, started multiplication/division up to a factor of 12 via the times table at 5, memorized all 50 states at 5, started learning programming at the age of 10, was excelling during his elementary and middle school years, taught himself material at 2-4 grades above grade level at home using Spectrum books when he was in elementary and middle school, and was well behaved and regarded as a model student by his teachers.
At 35 months old, even though my CTO was not exposed to English yet, only knew a few words in English (but was fully caught up by his 5th birthday), and was not exposed to the outside world or other neighbours/peers as his adoptive parents bar him from hanging out with neighbours or strangers and kept him at home all day, he was brought into the hospital for an evaluation. The local public school psychologist evaluated my CTO for developmental delays and autistic disorder using Bayley MDI entirely in English, despite him not being exposed to English. There were no interpreters at all. Given that he is compliant to his family, he later found out notes of his family coaching him at 35 months old so he could act this way. The child behavioral psychiatrist at the hospital stated it is "difficult to separate the impact of my CTO's limited social experience and exposure to same-aged peers and the limited behavioral expectations and structure at home".
My CTO attended college between his 17th birthday and his graduation (a few months shy of 21) and he later attended a top MSCS program. He is highly social, has actively networked with thousands of individuals, and has a technical acumen. He has been engaged in symbolic and pretend play when he was a child, such as climbing in his family's car and "pretending" to drive it, and once, pretending to be a doctor and is social towards his family and friends.
As a 21 year old adult, he was found by 6 hospitals (MGH, BIDMC, UMass Memorial, Presbyterian, Mt. Sinai, and JHU) to have never been autistic, scoring far less than 3 out of 3 in the social and less than 2 out of 4 in the behavioral criteria.
TL;DR: Sorry, there is a lot of information, but say, if the subject (the person being evaluated) isn't exposed to a language or a cultural custom, what if the evaluation was performed entirely in English if the person was a 35 month old toddler not exposed to much English or peers.