> "By next month I will have had run 50 km" - is there a BETTER way to say this sentence?
By next month, I will have run 50km. This means that "I run 50km" completes first, and then next month arrives afterwards.
> By my English textbook there's 16 tenses, 4x4
Depends on how you count tenses. Different textbooks will give different counts, depending on what is considered a "tense". Which is not a reflection of the complexity of English, but a reflection of how hard it is to come up with definitions for terms in linguistics. "Would" is often not counted as a tense, but it may be counted as a tense, particularly if you are explaining English to speakers of a language which have a tense expressing something similar.
> Point being, English grammar is far from simple, as this conversation clearly demonstrated
Most languages are far from simple, I don't think English deserves special attention.
By next month, I will have run 50km. This means that "I run 50km" completes first, and then next month arrives afterwards.
> By my English textbook there's 16 tenses, 4x4
Depends on how you count tenses. Different textbooks will give different counts, depending on what is considered a "tense". Which is not a reflection of the complexity of English, but a reflection of how hard it is to come up with definitions for terms in linguistics. "Would" is often not counted as a tense, but it may be counted as a tense, particularly if you are explaining English to speakers of a language which have a tense expressing something similar.
> Point being, English grammar is far from simple, as this conversation clearly demonstrated
Most languages are far from simple, I don't think English deserves special attention.