Learn Romanian: Drumul acesta e extrem de periculos iarna. - This road is extremely dangerous in winter.

Both mean "this road" and are perfectly fine to use! When the demonstrative (this) comes before the noun, the noun doesn't take an article (acest drum). When it comes after the noun, the noun must take the definite article (drumul acesta). Placing it after the noun is very common in everyday spoken Romanian.

Why do we need de in extrem de periculos?

In Romanian, adverbs of degree like extrem (extremely), destul (quite/enough), and extraordinar (extraordinarily) require the preposition de before the adjective they modify. You cannot just say extrem periculos, it must be linked with de.

Wait, drum is a neuter noun. Why does periculos look masculine?

Neuter nouns in Romanian behave like masculine nouns in the singular and feminine nouns in the plural. Since drum is singular here, the adjective periculos takes the masculine/neuter singular form. If it were plural, it would use the feminine plural form: drumurile sunt periculoase.

Why does iarna mean "in winter"? Shouldn't there be a preposition like "în"?

For seasons and parts of the day, Romanian often uses the definite form of the noun as an adverb to mean "during the...". So iarna literally means "the winter", but when used as a time marker in a sentence like this, it means "in winter" or "during wintertime".