In HTML output of RMarkdown document, it adds tooltips to code chunks which show their language. Uses https://atomiks.github.io/tippyjs/

example.Rmd

---
title: "Code chunks language tooltips"
output:
  html_document:
    theme: "united"
    self_contained: true
---

<!--You need to use Bootstrap theme (e.g. "united") to load dependencies. -->

```{r, child = "tooltip_child.Rmd"}
```

# R

```{r}
print("R")
```

# bash

```{bash}
echo "bash"
```

# Python

```{python}
print("Python")
```

# Render HTML

```{r, eval = FALSE}
rmarkdown::render("example.Rmd", output_file = "example.html")
```

tooltip_child.Rmd

<script src="https://unpkg.com/@popperjs/core@2"></script>
<script src="https://unpkg.com/tippy.js@6"></script>

```{js, echo = FALSE}
$(document).ready(function() {
  setTimeout(function() {
    $("code.hljs").each(function() {
      var pre = $(this).parent("pre");
      var lang = pre[0].classList[0];

      if (typeof lang !== "undefined") {
        // To modify the tooltip, look here: https://atomiks.github.io/tippyjs/v6/all-props/
        tippy(pre[0], {
          content: lang.toUpperCase(),
          placement: "left"
        });
      }
    });
  }, 250);
});
```