The main industries where interpreters are needed are: business, law, government, scientific / medical research and entertainment.
There are different requirements based on the nature of the material to be translated, but the main one is fluency in English and another language. Being fluent in more than one foreign language is always an advantage, as is knowing a rare dialect.
Spanish, French, German, Japanese and Chinese, just to name a few popular ones, are highly sought after in the translation and interpretation professions. But you can have an advantage if you study some less popular languages like Hebrew, Finnish, Dutch or Greek.
If you can find an area you like or at least like enough to work and evolve, try to see which countries and languages are strong in this field. The German has a lot of medical and pharmaceutical work, for example. They say that Japanese produces a good number of patents that need to be translated into English.
In the USA, the languages most in demand today are Arabic, Farsi / Dari, Chinese (Mandarin mainly), Japanese, Korean, Hindi, Urdu, German, French and Russian. Of course, Spanish is always in demand, but there are many natives who speak this language available.
The career opportunities always depend on the needs of those who hire. It is not just a specific language that may be in demand. There are many niche markets for those who have studied translation and interpretation and language competence is always a basic need and a trend in high demand.
Like any other trade, translation is a business. Someone has to pay for it, so if you are looking for a lot of job opportunities, look for languages in which many deals are made, such as Japanese, French, German and Spanish. Companies pay for most of the general translation and always need translated websites, applications, product reviews, customer emails, etc. Many startups also have a lot of money to pay for things to be translated into new markets.
In addition to the languages mentioned above, Mandarin and Portuguese will become increasingly important in the coming years due to growing economies and business growth prospects.