Which is more important for customer satisfaction, timely and good quality answers or local language support?

I think timely and quality answers are key components of customer satisfaction. There is no benefit to speaking with an agent who has little knowledge of the product/service (or who lacks the ability to solve issues) even if they speak the native language.

On a whole - this is an ill-posed question. We can construct multiple arguments/ scenarios/ use cases and bring out 1 facet over the other. Let me treat it as a question for forced prioritization.   Any communication system works because of 3 fundamental things - Sender, Medium and Receiver. We have the earnest customer (Receiver). “Timely and Good Quality Answers” refers to the actual solution of the query or grievance that customer has. Customer Support Rep has this solution (Sender). “Local Language Support” is property of Medium. Amongst the 3 fundamental things, we have the Customer (Receiver) – and we are asked to select between Sender and Medium. Hence, any choice will always be SUB-OPTIMAL. If forced to make a choice, I will always go with a Sender and Receiver. Languages can be related, a common language can prop-up and variety of other symbols and factors can bridge the language gap. But the agent brings the intelligence to the conversation – hence, critical.

I think both are inter dependent. When a customer support agent fails to provide quality and timely response and resolution, it matters least to which region he belongs to or whether he speaks the local language or not. IMO, As long as the customer is able to 'understand' the agent, the satisfaction level depends only on the skill of the agent, but not on the language proficiency. Sure, the first impression for the customer may not feel comfortable to deal with a non native speaker, but once he gets good quality response, it overcomes everything.

I have faced a lot this question about having locale support, and it has become a common concern in several companies, where the vision is not wide and there is a fear based on bad experience. As Jagant comments, these have no dependency between them. It is the knowledge and ability to solve issues what matters the most, we should encourage and foster the companies to change their thinking about this by focusing in accomplish SLA's and provide good resolutions.

A reasonable person would prefer correct answers from a non-native speaker.

In my opinion, both things are required for customer satisfaction but the most important thing is to provide them local language support first because it necessary to assure them about their problem.