Learn Hardcore Norwegian: Jeg planlegger enten å trene mer dette semesteret eller å studere mer. - I plan to either exercise more this semester or study more.

enten … eller corresponds to English either … or. You place enten before the first option and eller before the second. In this sentence it shows you have two possible plans:
– enten å trene mer (either to work out more)
– eller å studere mer (or to study more)

Why is the infinitive marker å repeated before studere? Could I drop it?

In Norwegian you may repeat å for clarity when you list two infinitives in parallel.
– More explicit: enten å trene mer eller å studere mer
– More economical (also correct): enten å trene mer eller studere mer
Repeating å simply makes the symmetry more obvious, but dropping the second å is allowed.

Why is it trene mer dette semesteret instead of trene dette semesteret mer?

Norwegian prefers the order: verb + adverb (mer) + time expression (dette semesteret).
– trene (verb)
– mer (how much? – adverb)
– dette semesteret (when? – adverbial phrase)
If you swap them you break the usual rhythm and it sounds odd to native ears.

Why use planlegger instead of skal? Aren’t they both about the future?

They’re not identical:
– skal can express the simple future or an obligation (I will / I must).
– planlegger (to plan) emphasizes intent or preparation: “I am planning to …”.
So jeg planlegger å trene mer means you have a considered plan, whereas jeg skal trene mer could be a bare statement of intent or even an order to yourself.

What exactly does mer mean here, and where does it go?

mer means more. As an adverb it modifies the verb that comes immediately before it. So trene mer = work out more (than you do now), and studere mer = study more. It always follows the infinitive in a clause like this.

Why is it dette semesteret (with a demonstrative and a definite ending) without a preposition like i?

When you say “this semester” in Norwegian you typically use the demonstrative + definite form: dette semesteret = “this semester.” Adding i (i dette semesteret) isn’t wrong, but Norwegians often drop it in casual speech:
– Jeg skal trene mer dette semesteret.
– Jeg skal trene mer i dette semesteret. (slightly more formal/explicit)

Why is the main verb in the present tense if this is a future plan?

In Norwegian (as in English) you often use the present tense to talk about scheduled or planned future activities, especially when you specify a time frame (like dette semesteret). The present here carries a sense of “I am planning right now for an action later.”

Does planlegge always require an infinitive clause with å?

Yes. planlegge is a transitive verb that needs an object. When that object is an action, you use the infinitive with å:
– planlegge + å + verb
Examples:
– Jeg planlegger å reise. (I plan to travel.)
– Han planlegger å kjøpe en bil. (He’s planning to buy a car.)