* Number of native speakers: This is the most common metric, but it's constantly changing. For example, Mandarin Chinese is usually considered the most spoken language by this metric.
* Total number of speakers: This includes native and non-native speakers, making languages like English much higher on the list.
* Number of speakers in a particular region: For example, Spanish might be the 4th most spoken language in North America, but it's not globally.
Therefore, you need to be more specific about what kind of "spoken" you're interested in to get an accurate answer.
Do you want to know the 4th most spoken language by:
* Native speakers?
* Total speakers?
* Speakers in a particular region?
Once you clarify your question, I can help you find the answer.