Sora mea merge la piață cu bicicleta când vremea este bună.

In Romanian, possessive adjectives like mea usually come after the noun, not before it.

So:

• sora mea = my sister
• fratele meu = my brother
• casa mea = my house

Putting mea before the noun would sound wrong in normal Romanian.

The base form is soră = sister.

When it becomes sora, that -a is the definite article attached to the end of the noun, so:

• soră = a sister / sister
• sora = the sister

Romanian usually says the sister my to mean my sister, so sora mea is the normal structure.

Yes. A merge is a general verb meaning to go, not only to walk.

So merge la piață cu bicicleta is perfectly natural and means goes to the market by bicycle.

If you want to say specifically goes on foot, Romanian often says:

• merge pe jos = goes on foot

The preposition la is commonly used for movement toward a place or destination.

So:

• merge la piață = goes to the market
• merge la școală = goes to school
• merge la magazin = goes to the shop

Here, piață means market. In other contexts, piață can also mean square, but here the meaning is clearly market.

Romanian usually does not use a separate word like English the. Instead, the definite article is attached to the noun.

But in la piață, the noun is not definite. It means something like to market or to the market in a general sense.

Romanian often leaves destination nouns indefinite in expressions like this, especially when the place is being mentioned as a common destination rather than as one very specific, identified place.

In Romanian, a very common way to express means of transport is:

cu + noun

So:

• cu bicicleta = by bicycle
• cu mașina = by car
• cu trenul = by train
• cu autobuzul = by bus

Even though cu often means with, in these cases it is the normal way to say by a means of transport.

That is just how Romanian normally builds this expression. With many means of transport, Romanian uses cu plus the definite form of the noun:

• cu bicicleta
• cu mașina
• cu trenul

So although bicicleta literally looks like the bicycle, the whole phrase simply means by bicycle.

This is something learners usually just have to get used to as a pattern.

Yes, pe bicicletă is possible, but it has a slightly different feel.

• cu bicicleta = the normal way to say by bicycle
• pe bicicletă = more literally on the bicycle

In many situations both can work, but cu bicicleta is the safer and more standard choice for expressing transportation.

Grammatically, când means when, but in this sentence it has a habitual meaning, so in English it is often understood as whenever.

Because the sentence describes a repeated action, când vremea este bună means something like:

• when the weather is good
• whenever the weather is good

Both ideas fit the Romanian sentence.

Vremea is the definite form of vreme.

• vreme = weather / time in some contexts
• vremea = the weather

Romanian normally says vremea when talking about the weather in general:

• Vremea este bună. = The weather is good.

So this is the normal form here.

Because bună has to agree with vremea, which is feminine singular.

Romanian adjectives agree in gender and number with the noun they describe.

So:

• timp bun = good weather/time if the noun is masculine
• vreme bună = good weather because vreme is feminine
• vremea este bună = the weather is good

They mean the same thing here.

• este = full form of is
• e = shorter, very common spoken form

So:

• vremea este bună
• vremea e bună

Both are correct. Este sounds a bit fuller or slightly more formal; e is very common in everyday speech.

Romanian present tense is often used for habitual or regular actions, just like English.

So this sentence does not mean she is going right now. It means this is something she generally does:

• Sora mea merge la piață... = My sister goes to the market...
• ...când vremea este bună. = ...when the weather is good.

So the whole sentence expresses a routine or repeated situation.

Yes. Romanian word order is fairly flexible, although the original sentence is a very natural neutral order.

You could also say:

• Când vremea este bună, sora mea merge la piață cu bicicleta.

This version puts more focus on the condition when the weather is good.

The original sentence and this reordered version mean essentially the same thing.