But learning the syntax is only a small part of learning a language. Knowing your libraries is a huge part of being productive. How do I do rest queries, cryptography, filesystem manipulations, serialization, spreadsheet manipulations, images manipulations, web frameworks, interaction with the OS, multi-threading debugging, UI, etc. Outside of staying within an ecosystem (JVM / .net), you need to rediscover all these from scratch, get bitten by all the gotchas, etc.
Exactly. Most people are proficient in 1/2 languages maybe, but in many cases, it is pretty common to be in a situation where you need ramp quickly to just understand stuff and make modest changes to the code when necessary. Don't really understand why people seem to make a big fuzz about it like it is a huge commitment.
Unpopular opinion stated, programming language as a skill by itself will gradually lose its importance in job market. Companies, specially big ones, will hire for domain experts, rather than language specialists.
The effort of learning new programming languages often seems to be hugely over-estimated.