Learn Hardcore Russian: Мне трудно молчать, когда видна такая красивая горная природа. - It is hard for me to keep silent when such beautiful mountain nature is visible.

dative + predicative + infinitive: Мне легко говорить по-русски.
not Я легко говорю по-русски (that would mean something different, more like “I speak Russian easily/fluently” and would usually need an adverb like легко modifying a verb that describes a more “skill-like” action).

What exactly is трудно here – an adverb or an adjective?

In this position трудно is a predicative word (often called a “category of state” in Russian grammar). It behaves a bit like:

жарко – it is hot
холодно – it is cold
можно – it is allowed / possible
нельзя – it is not allowed / impossible

So:

Мне трудно молчать. – It is hard for me to keep silent.

You can think of трудно here as something between an adverb and a short-form adjective, but you don’t need to change its form (no gender, no number) and it doesn’t agree with anything; it just describes the situation as a whole.

Why is the verb after трудно in the infinitive (молчать) and not conjugated like молчать → молчу?

The pattern кому + трудно / легко / интересно + infinitive is standard:

Мне трудно молчать. – It is hard for me to keep silent.
Ему легко говорить по-английски. – It is easy for him to speak English.
Им интересно читать. – They find it interesting to read.

If you conjugate the verb (я молчу), the sentence changes type:

Мне трудно молчать. – focuses on how hard the action in general is for me.
Я молчу. – just states the fact: I am silent / I keep silent.

Я трудно молчу is wrong because трудно doesn’t function here as a normal adverb modifying молчу. Difficulty is expressed by the impersonal pattern with the infinitive instead.

What is the nuance of молчать? Is it just “not to speak”?

Молчать means “to be silent, to keep silent, to not say anything.”

Nuances:

молчать – to be silent, to not speak (often with an idea of “choosing not to speak”)
не говорить – simply “to not speak / not talk”, more neutral
замолчать (perfective) – to fall silent, to stop speaking
умолкнуть (perfective, more literary) – to fall silent, become quiet

In Мне трудно молчать, the idea is:

“It’s hard for me to keep my mouth shut / to remain silent” (because the view is so beautiful that you want to say something about it).

Why is there a comma before когда?

In Russian, когда introduces a subordinate clause of time (“when”-clause). The rule is:

A main clause and a subordinate clause are separated by a comma.

Here:

Main clause: Мне трудно молчать
Subordinate clause: когда видна такая красивая горная природа

So we write:

Мне трудно молчать, когда видна такая красивая горная природа.

Who is the subject of видна? Why is видна feminine?

The grammatical subject is такая красивая горная природа.

Word order in Russian is flexible, so the subject can come after the verb:

видна такая красивая горная природа

природа is:

feminine
singular
nominative

видна is a short-form adjective (or predicative form) agreeing with природа:

masculine: виден (e.g. виден дом)
feminine: видна (e.g. видна гора)
neuter: видно (e.g. видно озеро)
plural: видны (e.g. видны горы)

So:

видна природа – “the nature is visible / can be seen”
and the adjectives and determiner come after видна but still agree with природа.

Why видна and not видно? I often see видно in Russian.

Both forms exist, but they are used differently:

видна – agrees with a specific feminine subject:
- Вдали видна гора. – A mountain is visible in the distance.
- Когда видна такая красивая горная природа… – when such beautiful mountain nature is visible…
видно – impersonal, neuter, often used without a specific subject:
- Вдали видно. – It is visible in the distance.
- Ничего не видно. – Nothing can be seen.

You could say:

когда видно такую красивую горную природу

This would sound more like an impersonal statement: “when one can see such beautiful mountain nature / when such beautiful mountain nature can be seen (in general).”

With видна … природа, we explicitly present природа as the subject; it sounds a bit more descriptive and literary.

What does такая красивая горная природа literally mean, and how do these adjectives work together?

Word by word:

такая – such (feminine singular)
красивая – beautiful (feminine singular)
горная – mountainous / mountain (adjective from гора – mountain)
природа – nature

So literally: “such beautiful mountain nature”.

About the adjectives:

All three (такая, красивая, горная) agree with природа in gender (fem.), number (sing.), and case (nominative).
Natural order here is from more general / emotional to more specific:
- такая (this kind of / such) → красивая (beautiful) → горная (mountain-related)

Горная природа is a common phrase meaning something like “mountain scenery / mountain landscapes / nature of the mountains” rather than just “mountains” as objects.

What case and gender is такая красивая горная природа, and why?

It’s in the nominative feminine singular, because it is the subject of the verb видна:

(Что?) природа – nominative, subject
такая, красивая, горная – all feminine singular nominative, agreeing with природа

If you changed the structure, the case would change. For example:

Я люблю такую красивую горную природу. – “I love such beautiful mountain nature.”
- Here такую красивую горную природу is accusative (object of люблю).

Could I say когда я вижу такую красивую горную природу instead of когда видна такая красивая горная природа? Is there a difference?

Yes, you can, and it is perfectly correct:

Мне трудно молчать, когда я вижу такую красивую горную природу.

Difference in nuance:

когда я вижу… – more direct, personal: “when I see such beautiful mountain nature.”
когда видна такая красивая горная природа… – more descriptive, slightly more literary: “when such beautiful mountain nature is visible / when such beautiful mountain scenery is in view.”

Both express essentially the same idea; the original is just a bit more “scenic” and impersonal in style.

Is there any difference between Мне трудно молчать and Мне тяжело молчать?

Both are very close and often interchangeable:

Мне трудно молчать. – It is hard for me to keep silent.
Мне тяжело молчать. – It is hard / heavy / burdensome for me to keep silent.

Nuance:

трудно – focuses slightly more on difficulty as a task or effort.
тяжело – adds a feeling of emotional or psychological heaviness.

In this sentence, both would sound natural.