Writing in ancient greek with Emacs and Linux

For starters, you want to write brother in ancient greek.

1. Type adelfos to get an understanding of what’s happening.
   
2. Set the input method to greek-babel: M-x set-input-method greek-babel.¹
   
3. Type adelfos again.
   

The last typing of “adelfos” results in αδελφοσ. So far so good.

However, αδελφοσ is wrong. It should be ἀδελφός. To be specific, we’re missing diacritics on a (alpha) and o (omicron) and the final s (sigma) is wrongly written as well.

We solve the problem by using combinations of letters, such as:
Typing >a results in ἀ
Typing 'o results in ό
Typing c results in ς

For completeness, type >adelf'oc in order to eventually get the desired ἀδελφός.

Good 🙂

Go back to your previous input-method via M-x toggle-input-method

Documentation

Read the documentation M-x describe-input-method greek-babel

Input method: greek-babel (‘BG’ in mode line) for Greek
  The TeX Babel input method for Classical Greek using mule-unicode-0100-24ff.

-------------------------------------
character     capital	      small
-------------------------------------
alpha		A		a
beta		B		b
gamma		G		g
delta		D		d
epsilon		E		e
zeta		Z		z
eta		H		h
theta		J		j
iota		I		i
kappa		K		k
lambda		L		l
mu		M		m
nu		N		n
xi		X		x
omicron		O		o
pi		P		p
rho		R		r
sigma		S		s
final sigma			c
tau		T		t
upsilon		U		u
phi		F		f
chi		Q		q
psi		Y		y
omega		W		w
-------------------------------------
sampi				!
digamma		#
stigma				$
koppa		&		%
-------------------------------------

------------------------
mark		key
------------------------
ypogegrammeni	|
psili		>
dasia		<
oxia		\='
koronis		\='\='
varia		\=`
perispomeni	~
dialytika	"
ano teleia	;
erotimatiko	?
----------------------

Optional - Increase readability

To increase the readability –of the in particular tiny diacritics–, you can enlarge the greek characters by doing the following:
Install the Gentium font: $ yay ttf-gentium
Evaluate this line or add it appropriately to your init.el:

(set-fontset-font "fontset-default" 'greek (font-spec :family "Gentium" :size 30))

Sources

https://stackoverflow.com/a/49765665/1172907
https://youtu.be/Fl4eu_bv54c?t=266