Learn Hardcore Russian: Если кабель слишком короткий, стоит заменить его. - If the cable is too short, it’s worth replacing it.

Если is the standard word for if in Russian and it typically introduces a condition (a subordinate clause): Если X, (то) Y = If X, (then) Y. It’s very commonly the first word of the sentence, but it doesn’t have to be; you can reorder: Стоит заменить его, если кабель слишком короткий.
In writing, the conditional clause is usually separated by a comma from the main clause.

Do I have to use то after the если-clause?

No. то is optional here.

Если кабель слишком короткий, стоит заменить его. (natural, neutral)
Если кабель слишком короткий, то стоит заменить его. (also natural; то adds a clearer “then” connection and can sound a bit more emphatic/structured)

Why is there a comma: Если ..., стоит ...?

Russian normally uses a comma between a subordinate clause introduced by если and the main clause. This is standard punctuation: Если [subordinate clause], [main clause].
If you reverse the order, you still keep the comma: Стоит заменить его, если кабель слишком короткий.

What does стоит + infinitive mean here? Is it about “cost”?

Here стоит is not about money. The pattern стоит + infinitive means it’s worth (doing) / it would be a good idea to (do) / one should (do) in a mild, recommendation-like way.
So стоит заменить = it’s worth replacing / it’s advisable to replace.

Why is стоит singular (and kind of impersonal)? Who “stands” or “costs”?

This is an impersonal construction. Russian often expresses recommendations without naming a subject. Think of it as “it’s worth…” with an implied это (“it”).
You can also make it more explicit: Если кабель слишком короткий, то его стоит заменить. (still impersonal, but more focused on его)

Is стоит заменить его the same as нужно заменить его or надо заменить его?

Not exactly. They differ in strength and tone:

стоит заменить = advisable / worth doing (softer, more like a suggestion)
надо заменить / нужно заменить = need to / must (stronger necessity; надо is more conversational, нужно more neutral/formal) So the original sentence is more of a recommendation than an obligation.

Why is it слишком короткий and not очень короткий?

слишком means too (more than desirable; a problem).
очень means very (just high degree, not necessarily a problem).
In context, a cable being too short is precisely the reason for the recommendation, so слишком fits.

Why is кабель masculine, and how do I know the adjective form короткий matches it?

кабель is masculine because it ends in a consonant in its dictionary form (кабель). In the nominative singular masculine, adjectives typically end in -ый / -ий / -ой.
So короткий кабель (masc. nom. sg.) matches correctly.

What case is кабель in, and why?

It’s nominative singular because it is the subject of the condition clause: кабель is what “is too short.”
Russian often omits the verb быть (“to be”) in the present tense, so кабель (есть) слишком короткий is understood as “the cable is too short.”

Why is его used, and what does it refer to?

его is the accusative-form object pronoun meaning him/it (and also his as a possessive, but not here). In this sentence it refers back to кабель (“cable”), so заменить его = “replace it.”

Is его really accusative? It looks the same as genitive.

Yes, for masculine/neuter singular его is used for both genitive and accusative in many contexts.
Here it’s accusative because it’s the direct object of заменить (to replace). The meaning and the verb’s requirements make the function clear.

Where can его go in the sentence? Could I say стоит его заменить?

Yes. Word order is flexible:

стоит заменить его (neutral)
стоит его заменить (also natural; puts a bit more focus on “it”)
его стоит заменить (even more topical: “as for it, it’s worth replacing”) All are grammatically fine; the choice is mostly about emphasis and style.

Why is the verb заменить perfective? Could I use заменять?

заменить is perfective and points to a complete, one-time result: “replace it (once, fully).” That fits typical advice about swapping a cable.
заменять is imperfective and would suggest process/repetition or general habit (“to be replacing / to replace in general”). In this concrete “do this once” situation, perfective заменить is preferred.

Is this a general statement (“whenever a cable is too short...”) or about one specific cable?

As written, it can be read both ways depending on context:

General advice: “If a cable is too short, it’s worth replacing it.”
Specific situation: “If the cable is too short, it’s worth replacing it.” If you want to make it clearly specific, you might add этот: Если этот кабель слишком короткий, стоит заменить его.
If you want it more general, you might pluralize: Если кабели слишком короткие, стоит заменить их.

Why is there no explicit “is” in кабель слишком короткий?

In the present tense Russian usually omits есть (“is”) in ordinary statements. So кабель слишком короткий literally “cable too short” is the normal way to say “the cable is too short.”
You may see есть for emphasis/contrast, but it’s not typical here.

Could I use короток instead of короткий?

Sometimes. короток is the short-form adjective (masculine) and can sound more formal/bookish or more “predicative” in tone.

кабель слишком короткий (common, neutral)
кабель слишком короток (also correct; slightly more formal/stylistic)
Both mean “the cable is too short.”

Would Russians ever say следует заменить его instead of стоит заменить его?

Yes. следует + infinitive means one should / it is advisable to and is more formal/official than стоит.

стоит заменить: everyday recommendation
следует заменить: more formal guideline/instruction