One of the features of the new One Search interface is the ability to change the display language.
Look up in the top corner of the white section at the top of the One Search page and you'll see the help and language controls.
By default, the language will be set to English (AU), but if you click on the arrow you'll see the range of languages you can chose from.
The "big guns" are there: Chinese, French, German, Spanish...
But there are also some languages from other parts of the world, like Malay, Finnish, Portuguese and Korean.
Changing your language options changes the display language in One Search (so all of your controls and options will change), but it does not change the ranking of the results. You will still see mostly English results at the top of your search.
To get search results in a language other than English, you could try using the Language filter at the bottom of the Refine Your Search section - but unfortunately One Search is not very good at figuring out what is and isn't in English.
The Language filter is not very reliable, and you will still find results in other languages.
If you really want to get results in a language other than English, the most reliable way is to use non-English keywords in your search.
But, if you want to change the display language to something more familiar, One Search may have your language as an option.