Brothels are legal in the Netherlands and must be licensed locally.
But the authorities are trying to tackle human trafficking and abuse.
ECJ rulings are binding throughout the 28-member EU.
"The court considers it is possible to require that a brothel owner be able to communicate in the same language with the prostitutes who work there," the ECJ said in a statement.
Only then could a brothel, including Amsterdam`s famous "shop windows", be organised to prevent abuses and criminal offences against the sex workers, it said.
Sex workers and sympathisers demonstrate in April 2015 against the closure of window brothels by the municipality in the red light district in Amsterdam.Image copyrightGetty Images
Image caption
Sex workers and sympathisers protested in Amsterdam in April against plans to limit window prostitution in an anti-crime push
An Amsterdam window prostitute and blogger, who uses the pseudonym Felicia Anna, told the BBC communication was key to fighting issues such as trafficking.
However, she said most of the sex workers she knew already communicated with brothel owners - as well as clients and law enforcement - in second languages such as Dutch or English.
She said new rules over the languages spoken would stop women who did not speak Dutch or English renting legal window spaces - seen as safer than illegal street prostitution.
`Public interest`
Thursday`s ruling comes after the authorities in Amsterdam refused to grant new permits to a brothel owner who rents windows to prostitutes in the city`s red light district.
The court said the decision was justified because he could not speak Hungarian or Bulgarian - the prostitutes` languages - to ask them whether they had been trafficked or forced to sell sex.
The brothel owner said he could use interpreters or online translation software instead.
He invoked EU single market rules, saying Amsterdam`s mayor, who is not named in the case, was being "discriminatory" and "disproportionate".
But the ECJ rejected this, citing "overriding reasons relating to the public interest".
Prostitution was legalised in the Netherlands and in Germany in 2002.
Under Dutch law, those working in the trade have to register at the chamber of commerce and pay tax.
But officials have tried to tighten up practices in Amsterdam in recent years, in an effort to combat human trafficking and organised crime.
It has been reported that around three-quarters of the women who work in the city`s sex industry are foreign, arriving mainly from Eastern Europe, Africa or Asia.
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