Automatically extract translatable strings from Xcode storyboards and update .strings files. Original version: https://gist.github.com/ole/5007019. Updated for Xcode 10 & Swift 4.2

update_storyboard_strings.sh

#!/bin/sh
#
# update_storyboard_strings.sh - automatically extract translatable strings from storyboards and update strings files updated for Xcode 10.1 & Swift 4.2

# Original script — https://gist.github.com/ole/5007019

# Folder structure to eliminate duplicates & to make xib localization work.
# Instruction:
# 1. Go to XIB / Storyboard, check out right bar (Inspector), go to Localization and check out desired language.
# 2. Create Localizable.strings file @ LANGUAGECODE.lproj with localized strings. (// TODO: Make it global)
# 3. Build.

# ****************************
#       FOLDER STRUCTURE
# ****************************
# |Storyboard folder
# |---| Base.lproj
# |---|--- FILE.storyboard
# |---| LANGUAGECODE.lproj
# |---|--- Localizable.strings
# | Folder
# |---| Base.lproj
# |---|--- FILE.xib
# |---| LANGUAGECODE.lproj
# |---|--- Localizable.strings
# ****************************
#    FOLDER STRUCTURE END
# ****************************

storyboardExt=".storyboard"
xibExt=".xib"
stringsExt=".strings"
newStringsExt=".strings.new"
oldStringsExt=".strings.old"
bakStringsExt=".strings--"
localeDirExt=".lproj"

oldIFS=$IFS
IFS=$'\n'

# Find storyboard file full path inside project folder
for storyboardPath in `find . -name "*$storyboardExt" -print`
do
    # Get Base strings file full path
    baseStringsPath=$(echo "$storyboardPath" | sed "s/$storyboardExt/$stringsExt/")
    echo "Base storyboard's string file path: "$baseStringsPath

    # Create base strings file if it doesn't exist
    if ! [ -f $baseStringsPath ]; then
        touch -r $storyboardPath $baseStringsPath
        # Make base strings file older than the storyboard file
        touch -A -01 $baseStringsPath
    fi

    # Only run, if storyboard's newer.
    if find $storyboardPath -prune -newer $baseStringsPath -print | grep -q .; then
        # Get storyboard file name and folder
        storyboardFile=$(basename "$storyboardPath")
        storyboardDir=$(dirname "$storyboardPath")
        echo "\nStoryboard File: $storyboardFile\n"

        # Get New Base strings file full path and strings file name
        newBaseStringsPath=$(echo "$storyboardPath" | sed "s/$storyboardExt/$newStringsExt/")
        stringsFile=$(basename "$baseStringsPath")

        echo "Extracting strings file"
        ibtool --export-strings-file $newBaseStringsPath $storyboardPath
                    # ibtool sometimes fails for unknown reasons with "Interface Builder could not open
                    # the document XXX because it does not exist."
                    # (maybe because Xcode is writing to the file at the same time?)
                    # In that case, abort the script.
                    if [[ $? -ne 0 ]] ; then
                        echo "Exiting due to ibtool error. Please run `killall -9 ibtoold` and try again."
                        exit 1
                    fi

                    # Only run iconv if $newBaseStringsPath exists to avoid overwriting existing
                    if [ -f $newBaseStringsPath ]; then
                        iconv -f UTF-16 -t UTF-8 $newBaseStringsPath > $baseStringsPath
                        rm $newBaseStringsPath
                        echo "Removing new file...\n"
                    fi

                    # Get all locale strings folder
                    for localeStringsDir in `find . -name "*$localeDirExt" -print`
                        do
                        echo "\n\nLocal string directory: $localeStringsDir\n"
                        # Base String File Path — базовый файл, из которого будет браться вся локаль.
                        baseStringFilePath="$localeStringsDir/Localizable""$stringsExt"
                        echo "Base strings file path: $baseStringFilePath"

                        # Storyboard folder
                        rp1=$(realpath $storyboardDir)
                        # Locale folder
                        rp2=$(realpath $localeStringsDir)

                        if [ -f "$baseStringFilePath" ]
                        then
                            echo "\n$baseStringFilePath found."
                            # Backing up Localizable.
                            cp $baseStringFilePath $localeStringsDir/../Localizable$stringsExt
                        else
                            echo "$baseStringFilePath not found."
                            # FILE NOT FOUND!
                            # Skip Base strings folder
                            if [ $rp2 == $rp1 ] || [[ $rp2 == *Base.lproj ]]
                            then
                                echo "Skip..."
                            else
                                echo $rp2
                                exit 1
                            fi
                        fi

                        if [ $rp1 != $rp2 ]
                        then
                            localeStringsPath=$localeStringsDir/$stringsFile
                            echo "Localized strings file: $localeStringsPath"

                            # If it doesn't exist -> Create. Don't forget to link it in pbxproj.
                                cp $baseStringsPath $localeStringsPath
                                echo "Created $localeStringsPath. Please link it to pbxproj."
                            oldLocaleStringsPath=$(echo "$localeStringsPath" | sed "s/$stringsExt/$oldStringsExt/")
                            echo "Temporary old file: $oldLocaleStringsPath"
                            cp $localeStringsPath $oldLocaleStringsPath

                            for string in $(cat "$baseStringFilePath")
                            do
                                # REGEX "*" = "*"
                                regex="\".*\".*=.*\".*\""
                                if [[ $string =~ $regex ]]
                                then
                                    IFS='='
                                    #      ARRAY
                                    STRINGS=()
                                    for innerString in $string
                                    do
                                        innerInnerString=$(echo $innerString | awk 'match($0, /\"([^\"]|\\\")*\"/) { print substr( $0, RSTART, RLENGTH )}')
                                        STRINGS+=($innerInnerString)
                                    done
                                    sed -i -- "s/${STRINGS[0]};$/${STRINGS[1]};/g" $localeStringsDir/*.strings
                                fi
                                IFS=$'\n'
                            done
                            rm $oldLocaleStringsPath
                        fi
                        # Restoring Base Localizable file
                        mv $localeStringsDir/../Localizable$stringsExt $baseStringFilePath
            done
    fi
done

# Cleaning...
find . -name "*$bakStringsExt" -exec rm -f {} \;
for stringFile in `find . -name "*$stringsExt" -print`
do
    storyboard=$(echo $(dirname "$stringFile")/../Base.lproj/$(basename "$stringFile" | cut -d. -f1)$storyboardExt)
    xib=$(echo $(dirname "$stringFile")/../Base.lproj/$(basename "$stringFile" | cut -d. -f1)$xibExt)
    baseName=$(basename "$stringFile" | cut -d. -f1)
    if [[ ( ! -f $storyboard ) && ( ! -f $xib ) && ! ( $baseName == "Localizable" || $baseName == "InfoPlist" ) ]]
    then
        rm $stringFile
        echo "Removed duplicate: $stringFile with basename: $baseName"
    fi
done

IFS=$oldIFS

Disclaimer: You shouldn't use it, unless you are trying to maintain a project which heavily relies on this script: https://gist.github.com/ole/5007019