Irrelevance of language works if you assume PLs to be more consistent, or abstractly-used than they are.<p>As soon as you need to squeeze out more (or even a little) performance, you need to know how the implementation works under the hood.<p>As soon as the languages abstractions begin to leak, you need a knowledge of the languages quirks and tells.<p>It takes a while to develop this experience, and there isn&#x27;t necessarily a great deal of overlap between PLs.