Yes, there is evidence that alkaline food affects internal pH, but it is important to note that the regulation of internal pH (acid-base homeostatis) has other contributing factors, which is why the impact of food is subtle.
I'm mainly aware of evidence from studies on sodium bicarbonate, as an example for a simple way to supplement alkaline food.
So technically you could say that alkaline food "helps to regulate internal pH", but it is a very weak influence. To emphasize the impact of other contributing factors to blood pH, it is also interesting to look at something like this:
M. Kox et al: Voluntary Activation of The Sympathetic Nervous System and Attenuation of the Innate Immune Response In Humans
This article studies the effect of the Wim Hof method, in particular its breathing technique. The breathing technique basically alternates between voluntary hyperventilation and breath holds. The supplementary material features a video of one subject performing the breathing technique, including monitoring of blood pH over the course of the exercise. The subject has a basline blood pH of 7.4. During hyperventilation, blood pH increases over 7.6 as a result of the reduced carbon dioxide levels in the blood. During breath retention, carbon dioxide levels normalize and the blood pH falls (almost) back to the baseline level. Note that these effects on pH are very quick compared to nutritional influences.
This example shows why it is difficult to separate the effect from alkaline food from other factors contributing to pH homeostasis. Taking a few deep breaths or holding your breath has a very immediate effect on blood pH, which can easily bias the more subtle effect from an alkaline diet. I'm not an expert, but I could imagine that the respiratory rate is even determined by dietary factors. Thus, instead of studying the effect on internal pH, it might be more sensible to show that an alkaline diet leads to reduced breathing in the long term, because the body could maintain the same pH level even with higher carbon dioxide levels.