Riddles by Gnomie
Four unclued solutions, three of them translated from the original and one which is the work's title, are given as the answers to riddles in a work. The first and last lines of an aria from the work appear in the grid. The wordplay of every clue produces an additional letter that is not needed for the solution. These, read in clue order, give a further instruction.
Across
1 Formal proclamation sadly ruins a component (14)
11 Only brief expression of approval for system of sherry production (6)
12 Area gurus adjusted for bard's diviners (8)
15 Fashions for wry faces long ago (4)
17 A reprehensible senior journalist humbled (6)
18 Wretched little person getting round umpire on the quiet (8, 2 words)
19 Beasts' enclosure unserviceable for family of birds (5)
21 Main, central area of church company reviewed (5)
23 Of an inferior quality that's hot, deep-fried Indian bread (5)
24 Aloofly now and then assume horizontal position for skateboard trick (5)
25 Believer in taxonomic theories equipped international coterie (7)
28 Endure tasteless odds and ends in small yard (4)
31 Philosophical belief including obscenity in fact according to Voltaire (7, 2 words)
33 Israeli monetary unit in ancient market places (5)
39 Window to the sky, mostly related to gospel writer (5)
40 Runs and several series of balls for player with no fixed position (5)
44 Descendant to become weary about cloth of gold (6)
46 Leader of technicians going into 'how' in promotional leaflet for stage contraption (8)
47 In Holyrood, purposes of upset drink left finally by the French (6)
48 Building material of constructed basements etc - to seal principally (14, 2 words)
Down
2 Shelter mostly and portable winch set up for Perth's vehicle protection (6, 2 words)
3 With no limits tools rear and endlessly trim a daisy tree (7)
4 Surprisingly surer about grand impulses (5)
5 Aborigine’s food plant spread up to front entry (6)
6 Cotton company clothing Carroll's heroine (6)
7 American heroin casually turning up in cooking ranges (4)
8 Actor with no words to speak welcomes first of roles as Bard's wall (4)
9 Heather's anger over upset resin (5)
10 Entire ley strangely where growth of timber stops (8, 2 words)
11 Little boats' special promenades essentially prescribed on aft and fore of ship (11, 2 words)
13 Disconcert one in Nice born to ramble (7)
14 Openly distrustful, circling Israel in a strange and frightening manner (6)
16 Severest crit, perversely, for slogans of hawkers (11, 2 words)
20 Tune down, somewhat and bring to nothing (4)
22 Closely united but not initially celebrated (5)
23 Small bottle containing bit of pilgrims' bo tree (5)
26 Following stage of journey, returning, sell up for jokes (8)
27 Of castle constructed of mineral found in dolomitic limestone, say (7)
29 A fine South American city hairdo (4)
30 Functioning in commotion at regular intervals (6)
32 Mostly fooled about average small depression (7)
35 At a subsequent time getting into old style westerns (6)
36 As a gamble cutting back one special recipe (6, 2 words)
37 Vigour and spirit in Ed's magical, medicinal plant (6)
38 Produced dull surface on coarse metal (5)
40 Rambling detour's the road to take (5)
42 Old white gannet turning up in inner temple (4)
43 Arrange to pour water on Ian's fag end (4)
