the implementation of tcl is not small; it's 1.9 megabytes stripped, 8.5 times the size of lua 5.2, which is a very popular embeddable scripting language:

: ~; ls -l /lib/x86_64-linux-gnu/libtcl8.6.so /lib/x86_64-linux-gnu/liblua5.2.so.0.0.0
-rw-r--r-- 1 root root 216960 Dec 10 2022 /lib/x86_64-linux-gnu/liblua5.2.so.0.0.0
-rw-r--r-- 1 root root 1852968 Feb 1 2023 /lib/x86_64-linux-gnu/libtcl8.6.so

even guile is smaller:

: bin; ls -l /lib/x86_64-linux-gnu/libguile-3.0.so.1.5.0
-rw-r--r-- 1 root root 1303112 Mar 5 2022 /lib/x86_64-linux-gnu/libguile-3.0.so.1.5.0

a small scripting language might be the 7th edition bourne shell or the 7th edition awk:

: bin; ls -l sh awk
-rwxr-xr-x 1 user user 46126 May 11 1979 awk
-rwxr-xr-x 1 user user 17310 May 5 1979 sh

admittedly tcl is still not as bloated as perl or cpython:

: bin; ls -l /lib/x86_64-linux-gnu/libpython3.11.so.1.0 /lib/x86_64-linux-gnu/libperl.so.5.36.0
-rw-r--r-- 1 root root 3823936 Nov 25 2023 /lib/x86_64-linux-gnu/libperl.so.5.36.0
-rw-r--r-- 1 root root 7732544 May 2 08:59 /lib/x86_64-linux-gnu/libpython3.11.so.1.0

and, at 47 megabytes, javascript makes even cpython look slim:

: Downloads; ls -l /usr/lib/x86_64-linux-gnu/libnode.so.108
-rw-r--r-- 1 root root 47166144 Jun 22 09:21 /usr/lib/x86_64-linux-gnu/libnode.so.108

which is almost as big as java's 187 megs:

: ~; du -sk /usr/lib/jvm/java-17-openjdk-amd64/lib/
187208 /usr/lib/jvm/java-17-openjdk-amd64/lib/

a small embeddable lisp might be xlisp or siod. or, in modern times, tinyscheme, which is a 103-kilobyte executable:

: Downloads; ls -l /usr/bin/tinyscheme
-rwxr-xr-x 1 root root 102648 Jun 8 2020 /usr/bin/tinyscheme

though to be perfectly fair we ought to include its standard library:

: Downloads; ls -l /usr/lib/tinyscheme/init.scm
-rw-r--r-- 1 root root 23806 Jun 8 2020 /usr/lib/tinyscheme/init.scm

which brings the total for tinyscheme up to 125k. siod and xlisp are easy to embed, but i haven't tried embedding tinyscheme in a c program, so maybe it's more of a pain than i imagine it would be

really small would be a forth. forth is basically a scripting layer for assembly language with an interactive shell and ide, and there are plenty of full-featured forths that will run in 16k of ram. unfortunately forth code is hard to read and easy to crash

garbage-collected pointer-graph languages like lisp, python, js, and perl5 tend to use a lot more runtime memory for a given amount of functionality; in tcl (or the bourne shell) a list of 10 numbers like {8 2020 23806 102 7 3 11 5 36 86} is stored as a string which might occupy 31 bytes, plus an allocation header of probably another 16 bytes on a 64-bit system, for a total of maybe 48 or 64 bytes. by contrast, in a lisp system each list item occupies a 16-byte cons cell, so you end up paying 160 bytes; and storage is not reclaimed promptly, so you typically have another multiplier of 1½–3 to keep from spending all your time in the garbage collector. lua is the same; perl and python are different in detail (usually reclaiming storage more promptly due to reference counting, but wasting space on reference-count fields, boxing integers in python's case, and bloated svs in perl's case) but broadly similar in outline

tracing garbage collection (as opposed to the much slower reference counting used by perl and cpython) tends to diminish easy embeddability, both because it's very tricky to do in standard c, and because it kind of wants to own your program's entire memory space

this stuff still matters a lot due to things like icache misses, embedded systems, and standalone executable size. people complain about the size of golang and rust binaries but they don't hold a candle to the cpython interpreter. but it mattered a lot more in the 90s!