La vendedora me dejó entrar al probador y comprobó que mi talla es mediana.

It means “she let me go in.” The pattern is:

• dejar + [person] + infinitive: La vendedora me dejó entrar.
• You can also attach the clitic to the infinitive: La vendedora dejó entrarme (less common but correct).
• A more formal alternative is permitir: La vendedora me permitió entrar.
• Another equivalent structure is dejar que + subjunctive, but then you don’t use the object pronoun: La vendedora dejó que (yo) entrara. Avoid “me dejó que entrara.”

Tip: dejar de + infinitive means “to stop doing” (e.g., dejó de fumar), which is unrelated here.

In Latin America, entrar a is very common, and a + el contracts to al. In Spain, entrar en is more common. All of these are correct:

• entrar al probador (LatAm preference)
• entrar en el probador (Spain preference)
• entrar a el probador is incorrect because you must contract to al.

Probador is a fitting/changing room in a clothing store. Common alternatives in Latin America:

• vestidor (also very common on store signage)
• Less commonly for stores, camerino tends to be a backstage dressing room. You’ll see signs saying Probadores or Vestidores.

They’re third-person singular preterite forms and are stressed on the last syllable:

• dejó (from dejar)
• comprobó (from comprobar) The accent marks indicate the correct stress and distinguish them from present-tense forms like deja and comprueba.

Both are possible:

• …comprobó que mi talla es mediana: emphasizes that the result is still valid now.
• …comprobó que mi talla era mediana: frames it within the past context. With comprobar (“to confirm/verify”), the subordinate clause usually takes the indicative, not the subjunctive, because it asserts a fact.

Because talla is feminine, the adjective agrees: talla mediana.

• mediano/mediana = medium-sized.
• medio usually means “half” or functions as an adverb (“kind of”), not a clothing size.

No:

• comprobar = to check/confirm/verify a fact (e.g., comprobar que la talla es mediana).
• probar = to try/taste/test.
• probarse = to try on clothing (reflexive), e.g., me probé la camisa.

Yes, with nuances:

• verificó / confirmó: close to comprobó (formal/neutral).
• revisó: “looked over/checked,” not always implying confirmation of a fact.
• chequeó (many countries) / chequeó/chequeó vs checó/checó (Mexico often says checar/checó): informal/colloquial “checked.”

With dejar + infinitive, the person is typically the direct object. For 1st/2nd person, the form me/te/nos/os doesn’t show the difference. In third person:

• Standard in Latin America: La vendedora lo/la dejó entrar.
• In Spain, leísmo is common and accepted: La vendedora le dejó entrar (masculine human referent).

Yes. Both are correct:

• Me dejó entrar al probador (more common).
• Dejó entrarme al probador (also fine).

Because with dejar que, you must use the subjunctive without the clitic object:

• Correct: Dejó que (yo) entrara.
• Correct: Me dejó entrar.
• Incorrect: Me dejó que entrar.

No. That’s dequeísmo. Use:

• comprobar que (no “de”): comprobó que mi talla es mediana. But some verbs do take de que, e.g., asegurarse de que: Se aseguró de que todo estuviera listo.

Size as an inherent attribute uses ser: Mi talla es mediana. You use estar/quedar for fit in the moment:

• Esta camisa me queda grande/chica.
• Not: “Mi talla está mediana.”

Yes, but it changes the meaning:

• al probador = to the (specific) fitting room.
• a un probador = to a fitting room (unspecified/one of them).

Vendedora is a female salesperson. Alternatives:

• vendedor (male), vendedora (female).
• dependiente/a (common in Spain).
• empleado/a (employee; generic).
• cajero/a (cashier), a different role.