Public/Translation/Invoke-BackTranslation.ps1
|
function Invoke-BackTranslation { <# .SYNOPSIS Translates a subtitle file back to the source language to verify translation quality. .DESCRIPTION Takes a translated SubtitleFile, re-translates it back to the source language using an AI provider, and returns a comparison report showing each entry's original text alongside the back-translation. Significant divergence between original and back-translated text indicates potential mistranslation or meaning loss. .PARAMETER TranslatedFile The translated SubtitleFile to verify. .PARAMETER OriginalFile The original source SubtitleFile to compare against. .PARAMETER BackLanguage The language to translate back to (usually the source language, e.g. 'en'). .PARAMETER ProviderName AI provider for back-translation. .PARAMETER Session An existing translation session. .PARAMETER SimilarityThreshold Entries with word-overlap below this threshold (0.0-1.0) are flagged as potential issues. Default: 0.5. .EXAMPLE $original = Import-SubtitleFile 'movie.srt' $translated = $original | Invoke-SubtitleTranslation -TargetLanguage 'fa' -ProviderName Anthropic $report = Invoke-BackTranslation -TranslatedFile $translated -OriginalFile $original ` -BackLanguage 'en' -ProviderName Anthropic $report | Where-Object { $_.Flagged } | Format-Table -AutoSize #> [CmdletBinding()] [OutputType([PSCustomObject[]])] param( [Parameter(Mandatory)] [SubtitleFile] $TranslatedFile, [Parameter(Mandatory)] [SubtitleFile] $OriginalFile, [Parameter(Mandatory)] [string] $BackLanguage, [ValidateSet('OpenAI', 'Anthropic', 'Google', 'OpenRouter')] [string] $ProviderName, [hashtable] $Session, [double] $SimilarityThreshold = 0.5 ) # Build a session if not provided if (-not $Session) { if (-not $ProviderName) { throw 'Specify -ProviderName or pass -Session.' } $Session = New-TranslationSession -ProviderName $ProviderName } Write-Verbose "Back-translating $($TranslatedFile.Entries.Count) entries to '$BackLanguage'..." Write-Progress -Id 1 -Activity 'Back-translation verification' -Status 'Translating...' -PercentComplete 0 # -ProgressParentId 1 nests Invoke-SubtitleTranslation's own bar (-Id 2, and # its priming phase at -Id 3) beneath this function's bar instead of the two # colliding at the same top-level id. # -NoSummary: the back-translation is an internal verification pass, not the # caller's deliverable. Printing "Translation complete" here would describe work # the caller did not ask for, above the similarity report that they did. $backTranslated = Invoke-SubtitleTranslation ` -InputObject $TranslatedFile ` -TargetLanguage $BackLanguage ` -Session $Session ` -ProgressParentId 1 ` -NoSummary Write-Progress -Id 1 -Activity 'Back-translation verification' -Status 'Comparing...' -PercentComplete 80 $report = [System.Collections.Generic.List[PSCustomObject]]::new() $maxIndex = [Math]::Min($OriginalFile.Entries.Count, $backTranslated.Entries.Count) for ($i = 0; $i -lt $maxIndex; $i++) { $origEntry = $OriginalFile.Entries[$i] $transEntry = $TranslatedFile.Entries[$i] $backEntry = $backTranslated.Entries[$i] $origText = ($origEntry.Lines -join ' ').ToLower() -replace '[^a-z0-9 ]', '' $backText = ($backEntry.Lines -join ' ').ToLower() -replace '[^a-z0-9 ]', '' # Simple word-overlap similarity $origWords = $origText -split '\s+' | Where-Object { $_ } $backWords = $backText -split '\s+' | Where-Object { $_ } $union = (@($origWords) + @($backWords) | Sort-Object -Unique).Count $intersect = $origWords | Where-Object { $backWords -contains $_ } $similarity = if ($union -gt 0) { $intersect.Count / $union } else { 1.0 } $report.Add([PSCustomObject]@{ Index = $origEntry.Index Start = $origEntry.Start OriginalText = $origEntry.Lines -join ' / ' TranslatedText = $transEntry.Lines -join ' / ' BackTranslation = $backEntry.Lines -join ' / ' Similarity = [Math]::Round($similarity, 2) Flagged = $similarity -lt $SimilarityThreshold }) } Write-Progress -Id 1 -Activity 'Back-translation verification' -Completed $flagged = ($report | Where-Object { $_.Flagged }).Count Write-Verbose "Back-translation complete. $flagged / $($report.Count) entries flagged (similarity < $SimilarityThreshold)." return $report.ToArray() } |