Is the word janta the same in Brazilian and European Portuguese?

No

While the two words share the same root, there is a difference in typical usage. In Brazilian Portuguese, "janta" is a very common, colloquial noun used to refer to the evening meal (a shortened version of jantar). In Continental Portuguese, the noun for the evening meal is "o jantar." While a person from Portugal would understand "janta" due to the influence of Brazilian media, they would not use it naturally; using "janta" in Portugal would sound distinctly Brazilian or even incorrect to a local ear.

Brazilian Portuguese Examples

1. A janta está pronta! (Dinner is ready!)
2. O que tem para a janta hoje? (What is there for dinner today?)
3. Eu esqueci de preparar a janta. (I forgot to prepare dinner.)
4. A janta de ontem estava uma delícia. (Yesterday's dinner was delicious.)
5. Vamos fazer uma janta especial hoje à noite. (Let's make a special dinner tonight.)

Continental Portuguese Examples

1. O jantar está pronto! (Dinner is ready!)
2. O que é que há para o jantar hoje? (What is there for dinner today?)
3. Esqueci-me de preparar o jantar. (I forgot to prepare dinner.)
4. O jantar de ontem estava uma delícia. (Yesterday's dinner was delicious.)
5. Vamos preparar um jantar especial hoje à noite. (Let's prepare a special dinner tonight.)