Along with the fun example of inventing a future tense inflection in English, we might want to compare English with one or more (non-Germanic but still related) languages that clearly do have a future tense:
English: I will speak vs. French: je parlerai
English: I would speak vs. French: je parlerais
In this example, English conveys the sense of future certainty or more general possibility through the two-part construction of the modal auxiliary will/would (in its present or past form) and the infinitive speak. In French, the regular verb parler itself is modified (taking on an inflectional ending -ai/-ais).
Of course, I'm pretty sure that, no matter what the contemporary linguists say, young English speakers across the US or even around the world are being taught that "I will speak" is an example of future tense in English.
As a side note, English can also show futurity through the simple use of the present tense and an adverb of time:
Today we feast. Tomorrow we die.
English has two specifiable tenses: past formed with -ed or -t verbal inflections and present formed with -s/es verbal inflections in 3rd person singular. Past and present tenses can be modified by aspect: progressive and perfective affecting past and present tense and future construction. Future constructions are said not to be a construct of tense because there is no inflection for futurity in English: there is no -something to add to a verb to render it recognizable as a word inflected in the future tense.
Just for discussion, let's invent such an inflection. Just for discussion, let's say -inc is the inflection that affixes to English verbs to form future tense. We'd then have things like, "Billy runinc next week." Tenses would then follow this order, "Billy ran last week," "Billy runs today," "Billy runinc next week." "Billy runs often!" Or we might have, "I ran; I run; I runinc." I think this fun example shows that there is no future tense in English and why there is not.
Futurity in English is constructed (1) with the modal verb will + base infinitive verb: will run (to run) or (2) with present (tense) progressive (aspect): be (is/am/are) + going + infinitive verb: is going to run; am going to run; are going to run.
To me, this is simply a semantic issue. There clearly is a future tense in English, but we do not use an inflection of the verb to create a future tense. However, when we say "I will type an answer to this question" we know that the action will take place in the future.
Sure, we don't have a verb form for the future in the same way that Spanish does (for example), but we do have a construction that makes it clear that an action will happen in the future.